LSAA 2007 Conference and Design Awards
LIGHTWEIGHT ARCHITECTURE
Stretching Our Boundaries Internationally
Crowne Plaza, Surfers Paradise October 25–26 2007
PROCEEDINGS
Edited by Peter Kneen Lightweight Architecture Stretching Our Boundaries Internationally
Proceedings of the 2007 Conference Lightweight Structures Association of Australasia
SURFERS PARADISE – OCTOBER 25, 26 2007
Supported by: Major Sponsors: Mehler and Ferrari Silver Sponsors: Ronstan, Pacific Computing and Hiraoka
EDITOR: PETER KNEEN
COPYRIGHT NOTICE Apart from any fair dealing for the purposes of private study, research, criticism or review as permitted under the Copyright Act, no part of these proceedings may be reproduced by any process without written permission. Copyright for each contributed paper remains with the authors. The Publisher does not accept any responsibility for any breach of copyright with respect to material supplied by the authors.
The Editor does not accept resonsibility for statements made by contributing authors. Lightweight Architecture Stretching Our Boundaries Internationally
PREFACE
The Lightweight Structures Association is an autonomous, inter–disciplinary group of interested parties involved in the field of lightweight structures with the basic aim of promoting the proper application of lightweight structures, their design, fabrication, construction and materials, and the development of these and other aspects particular to lightweight structures. Details of our objectives, membership categories and member profiles can be found on our website www.lsaa.org Lightweight structures are widely employed in architecture, engineering and building construction and find application in long span roofs for stadiums and exhibition structures; covered shopping malls; entrance structures; signature structures and sculptures as well as shade and environmental protection canopies. The shape of a lightweight structure is determined through an optimisation process to efficiently carry the loads from a critical loading case. They are recognised for their aesthetic appearance, technical excellence in design, efficient use of modern technology and their innovative character. Last year the LSAA celebrated 25 years. When it started, the lightweight structures industry was in its infancy and we developed our design and fabrication skills largely in isolation from the rest of the world. Today, our members stand proudly on the world stage and regularly design and construct significant lightweight structures in all parts of Asia, the Middle East, Europe, the Americas and other corners of the globe. A distinguished group of keynote and other speakers have been assembled to present experiences of our quest to ”Stretch our Boundaries Internationally”.
LSAA Design Awards 2007
The presentation of the LSAA 2007 Design Awards will take place at the Conference Dinner at 19.00 on Thursday night. The Design Awards given in recognition of excellence in design, construction and application of Lightweight Structures. Entries in the four categories are invited from individuals, companies and institutions. H SMALL STRUCTURES Project area less than 250 sqm H MEDIUM STRUCTURES between 250 sqm and 1,000 sqm H LARGE STRUCTURES Project area exceeds 1,000 sqm H SPECIAL APPLICATIONS Website: http://www.lsaa.org
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CONTENTS
Program Thursday October 25 2007...... 4 Program Friday October 26 2007...... 5 Wembley Stadium...... 7 Sharm El Sheikh Airport Terminal Roofs...... 8 RAS Showgrounds Grand Pavilion...... 14 KEYNOTE ADDRESS...... 21 Learning from Nature...... 22 Structural Design and Optimisation of the Beijing National Aquatics Centre...... 30 Austrade’s Global Network – how to use it and the value it can bring to your business...... 43 Techniques and Solutions to Installation of Tensile Membrane Fabrics...... 44 Kuwait Airport VIP canopy...... 48 SILICONE COATED ARCHITECTURAL TEXTILES...... 52 Construction of Local and International Projects using EFTE...... 58 Update on Fire Testing for Tension Structure Fabrics in Australia, (and overseas developments)...... 79 A Regulator’s Dilemma: Case Study...... 82 Flame Retardancy Disambiguation...... 83 Fabric Life – Expectations and Experience...... 85 Robina Stadium...... 96 Stretching the Boundaries of Membrane and Film: Robina Skilled Stadium and Clarke Quay...... 106 Project X experiences of multidisciplinary Arch/COFA/Eng teaching...... 112 A Briefing on European Masters Program & Workshops...... 120 Low Environmental Impact Fabric Structures...... 123 Wind Engineering for Lightweight Structures...... 125 Lightweight Structures – Where We Have Come from and Some Current Issues...... 136
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Program Thursday October 25 2007
08.00 Registration Desk Opens Session 1 ”Large Scale Projects” 09.00 Opening LSAA President: Kourosh Kayvani 09.10 Wembley Stadium – Kourosh Kayvani (Connell Wagner) 09.35 Sharm el Sheikh Airport – Joseph Dean (Wade Consulting) 10.00 RAS Melbourne Showgrounds Grand Pavilion – Peter Lim (Tensys) 10.25 Morning Tea / coffee Session 2 ”Bubblism” 10.55 Keynote Address Chris Bosse (Director, Visionary Architects, formerly with PTW) Computational Formfinding of Natural Organic Structures and Realized Projects including the Watercube with PTW 11.55 Structural and Environmental Design of the Beijing Water Cube – Mark Arkinstall (Arup) 12.20 Lunch Session 3 ” Local and OS Contracting Issues” 13.40 Austrade’s Global Network – how to use it and the value it can bring to your business Jeff Turner 14.00 Membrane Structures – Installation Techniques and Solutions – Dean Peters (OzRig) 14.20 Kuwait Airport VIP Canopy – Ian Norrie (VDM) 14.40 Construction of Local and International Projects using ETFE Angus Macleod (Vector) 15.00 Silicone Coated Glass Fabrics for Tensile Structures – James Dar (Sila Australia) 15.20 Afternoon Tea / coffee Session 4 ”The Fire and Material Issues” 15.40 Fire Tests and Developments in Europe Brian O’Flaherty (Indtex) 16.00 A Regulator’s Dilemma: Case Study John Shaw (BC Vic) 16.20 Flame Retardancy: Disambiquation – Paul Knox (Innova) 16.40 Fabric Life: Expectations and Experiences – Chris Tattersall 17.00 Day Closure and Announcements 17.15 LSAA AGM (Members) 18.30 Pre Dinner Drinks, LSAA Dinner & Design Awards
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Program Friday October 26 2007
08.30 Registration Desk Opens Session 5 ”Local Projects” 09.00 Invited Address Warrick Chalmers (Senior Associate HOK Sport Architects) Gold Coast Stadium Design Concepts and other Local Projects 09.45 Stretching the boundaries of membrane and film: Robina Stadium & Clarke Quay – Peter Lim (Tensys) 10.20 Session 6: Site Tour Buses to take attendees to the new Robina Stadium – home of the Gold Coast Titans Tour made possible with the assistance of Watpac Limited & Major Sports Facilities Authority Queensland Government. 12.30 Lunch Session 7 ”Design Skills and Knowledge” 14.00 Project X – Experiences of Multidisciplinary Arch/Eng/COFA Teaching – Zora Vrcelj (UNSW) 14.20 A briefing on the European Masters program; Tensinet, LSA and Ferrari study workshops 14.30 Low Environmental Impact Fabric Structures – Pierre Renard (Ferrari) 14.50 Wind Engineering for Lightweight Structures – Tony Rofail (Windtech Consultants). 15.10 Afternoon Tea / coffee Session 8 ”Industry Issues” 15.40 A look at where we have come from and current issues – Peter Kneen (LSAA) 16.00 Panel Session on Industry Issues including BCA changes, fire tests, education, questions from the floor – speakers to form panel 16.50 Conference wrap up 17.00 Conference Closure
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MAJOR SPONSORS H INDTEX – MEHLER H INNOVA – FERRARI
SILVER SPONSORS H RONSTAN H PACIFIC COMPUTING H HIRAOKA
EXHIBITORS S INDTEX – MEHLER S INNOVA – FERRARI S RONSTAN S PACIFIC COMPUTING S HIRAOKA S SILA AUSTRALIA S GALE PACIFIC
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Wembley Stadium
Dr Kourosh Kayvani Principal, Connell Wagner President LSAA
Summary Various aspects of the design and construction of the roof of the Wembley Stadium are presented.
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Sharm El Sheikh Airport Terminal Roofs
Joseph Dean Director – Wade Consulting Group Pty Ltd
(The following paper will be delivered with additional graphics to further illustrate the issues presented here and others – if additional information is required contact Joseph Dean, Wade Consulting Group, [email protected])
Introduction The Sharm el Sheikh Airport Terminal building roof in north east Egypt constitutes a landmark tensioned fabric structure. It is believed to be the first project in Egypt to use a two layer architectural membrane roof. Birdair were successful in winning the contract to provide the membrane roof, steel support framing and aluminium and glass skylight system. Wade Consulting Group was commissioned by Birdair in February 2005 to provide engineering final design and drawings for the steel framing and assistance with patterning and scheduling for the fabric, cables and fittings. The contract value for our services was between $150k and $200k which represents approximately 2.5% of the roof contract. This fee included performance and optimization bonuses. The time allowed for the bulk of the engineering design was approx four months. Apart from a slight delay in approvals coming back this was essentially achieved and we received a performance bonus on this basis. Project Details Project Name: Sharm el Sheikh International Airport Location: Sharm El Sheikh, Egypt Owner: The Egyptian Company for Airports Architect: dar al–handassah Roof Fabricator: Birdair General Contractor: Saudi Binladen Group
Total cover area: 15,700 m2 (168,993 sqf) Fabric area: 33,000 m2 (355,209 sqf)
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Year of completion: 2006
Membrane type: Outer Layer PTFE Sheerfill I Liner Fabrasorb I The terminal building comprises a central link building and arrival and departure halls. The central link building or ”boat” structure is concrete as are the perimeter ring beams and columns for the arrival and departure halls. The roofs of the arrival and departure halls have an outer layer of Sheerfill I and a Fabrasorb I liner separated by approximately 400 mm. The two layers of PTFE fabric are supported by steel and cable framing and aluminium extrusion at the perimeter are the subject of this discussion. The two halls are essentially 100 metres in diameter, the arrival hall is framed with arched steel trusses on columns while the departure hall features five steel rings supported by branching columns. Design The drawings we received indicated that a preliminary design for tender drawings had been done by Tensys Consultants and Tony Hogg Design. A tender pricing design check had also been undertaken by Birdair. This meant that much of the design work was fairly routine, confirming member sizes and further detailing the substantial connections. The roof structures were modelled and analysed using dedicated membrane and cable net finite element modelling software MCM / MCAP written by Martin Brown. Other in–house post processing software was used to refine the design. Some aspects of the steel framing were also modelled and checked in SpaceGass.
Reactions to the footings and perimeter ring beam were determined and provided to allow checking of the perimeter frame and footing design by the local concrete designer. Design work on the roof structures was carried out by us from April to August 2005. Design Challenges A significant design constraint imposed by the concrete support frame designers was that the arches for the arrivals hall were to impose no significant lateral thrust on the perimeter ring beam. To achieve this, a slotted hole was provided at the arch truss anchor points to allow this point to move horizontally in line with the truss.
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The preliminary design intent was that the fabric was to be fixed by bolt rope and extrusion to both the arch trusses and the concrete ring beam. The potential movement of the trusses relative to the concrete ring beam created a situation in the corner where the fabric could be very highly stressed by this relative movement. The solution we settled upon to overcome this difficulty was to provide a pivoting clamp beam approximately 4 metres long on either side of the truss end. This beam provided a transition zone for the fixed edge of the fabric between the movement at the end of the truss and the concrete edge beam.
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Extra Engineering Support The fabric is attached relatively symmetrically to each side of the arches trusses. The design of the top face of these trusses did not require fully triangulated truss action therefore no diagonals were included in the design. The fabricator chose to build these trusses on the side so when it came time to lift the trusses into place it was found that significant deflections would occur. We were asked to provide details and strengths of temporary rigging required to allow for safe lifting of the trusses. Analysis of the lift cases for single trusses were carried out and temporary diagonal chains, cables and steel were specified to allow the lift to take place safely. The lift to vertical was achieved by three cranes and the final positioning by one very large site crane.
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Further Comments While our design phase was targeted for four months the graph of hours spent on the job shows that the subsequent phases and unforseen assistance like support during erection etc added significantly to the cost of the engineering design. These elements should not be under estimated and we were fortunate to have a client in this case who valued good engineering support.
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Wade Consulting Team Director – Joseph Dean Senior Design Engineer – Andrew Row Drafting Manager – Paul Thomas Lead Drafter – Mark Bovill From our company point of view this represents a landmark project which we carried out quickly and to the complete satisfaction of our client.
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RAS Showgrounds Grand Pavilion
Peter Lim Tensys Engineers
Summary The Royal Melbourne Showgrounds has been a vital link between country and city throughout its 150–year history. To strengthen this tradition, the Government committed funding to redevelop the Ascot Vale site – one of Victoria’s much–loved landmarks. This redevelopment restored buildings and created new facilities. Environmentally sustainable designs were also used to deliver a quality, versatile exhibition precinct capable of hosting events and functions throughout the year as well as the Royal Melbourne Show. The project aimed to: H enhance the Melbourne show H improve the link between urban and rural Victoria H help Victoria’s agribusiness sector grow, and H create a flexible, multipurpose events and exhibition precinct The new buildings and facilities at the showgrounds include: H Grand Pavilion, providing 8,000 square metre of enclosed exhibition space H Town Square, providing 8,500 square metres of grassed public open space H a revitalised main entrance and Grand Boulevard H 10,000 square metre Exhibition Pavilion H 8,000 square metre Main Arena with 4,300 permanent seats Some of the heritage buildings which have been renovated and restored as part of the redevelopment include: H Centenary Hall, an art–deco hall built in 1934 H Public Grandstand, built in 1915 H the heritage–listed Pie in the Sky. Two–thirds of the 27–hectare site will be developed as a venue for the Royal Melbourne Show, while land on the eastern side of the site near Epsom Road is planned to be developed for possibly commercial and/or retail use.
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The future of the non–core land on the western side, near Langs Road, has not been finalised. The Royal Melbourne Show has been a major event for Victorians since 1853, successfully showcasing the best of rural and regional Victoria. The new Showgrounds will build on this history while contributing to the growth of the Victorian food and agribusiness sector and improving the understanding between city and country communities.
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The joint venture between the State and the Royal Agricultural Society of Victoria is overseeing the project which will be delivered under the State Government’s Partnerships Victoria policy. Any involvement by the private sector has been to best meet the project objectives and sustain the long term future of the Royal Melbourne Show. PPP Solutions, comprising Multiplex Infrastructure and Babcock & Brown, delivered the redevelopment works. Design Concepts – Overall and Mast tops H A large plan area approx 98m x 84m to be covered H Overlaying fabric over the area required some form of support H A multi conical fabric form was decided as a lightweight solution H Development and focus on 6 mast conic type structure
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Perimeter mast head details received considerable attention to reduce the bulk and permit erection webbing to be wrapped around the smaller diameter but extended mast heads as shown below.
Erection
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Final tensioning was done by jacking of the masts from the base.
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KEYNOTE ADDRESS
Chris Bosse Director Visionary Architects Formerley with PTW
Born in 1971 in Stuttgart, Chris Bosse was educated in Germany and Switzerland and worked in several European architecture firms. His postgraduate degree at the University of Stuttgart dealt with the implication of virtual worlds into architecture. With www.smoarchitektur.com (Mad Oreyzi) he developed the Bubble–Highrise for Berlin in 2002 (a+u 05:01). Since 2003 he has been working with PTW Architects in Sydney on many high–profile projects in China, Vietnam and Middle East. PTW has recently started a number of projects in various parts of Japan. The project for the National Swimming Center for Beijing 2008, called the Watercube, received the Atmosphere Award at the 9th Venice Biennale and is under construction since 2004. The MOËT Marquee in Melbourne explored his interest in unusual structures in a freeform interior based on the physics of champagne bubbles and minimal surfaces. The work is widely published and Chris guest–lectures at various universities. He has recently left PTW and started his own office with branches in Sydney and Dubai.
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Learning from Nature
The ”trend” of learning from nature has always been there. It currently experiences a renaissance through new computer–technologies. We have to differentiate between mimicking nature and learning from nature. Learning from the intelligence of nature, means lighter buildings, less waste of materials, more energy–efficiency and more natural environments. These happen to be naturally more beautiful, too. People like Antonio Gaudi and later Frei Otto have initiated an intelligent approach in learning from nature for their architecture. We continue this today with digital means. The Watercube The so–called WATERCUBE associates water as a structural and thematical ”leitmotiv” with the square, the primal shape of the house in Chinese tradition and mythology. The entire structure of the Watercube is based on a unique lightweight–construction, developed by PTW with ARUP, and derived from the structure of water in the state of aggregation of FOAM. Behind the totally randomized appearance hides a strict geometry as can be found in natural systems like crystals, cells and molecular structures – (the most efficient subdivision of 3dimensional space with equally sized cells.) By applying this novel material and technology the transparency and the appearing randomness is transposed into the inner and outer skins of ETFE cushions. Unlike traditional stadium structures with gigantic columns and beams, cables and backspans, to which a facade system is applied, in the Watercube design, the architectural space, structure and facade are one and the same element. Conceptually the square box and the interior spaces are carved out of an undefined cluster of foam bubbles, symbolizing a condition of nature that is transformed into a condition of culture. The appearance of the aquatic centre is therefore a ”cube of water molecules” – the WATERCUBE. In combination with the main Olympic stadium, a duality between fire and water, male and female, Yin and Yang is being created with all its associated tensions/attractions. Water and visual appearance One of the most interesting design elements of the Watercube project is its visual appearance. This is a building all about water. Water becomes a profound ’building material’ that de–materializes the building in a meaningful way. That is the molecular structure of water in its foam state is magnified into the structure of the building. The structure of water softens and dissolves all the boundaries, and gives the sophisticated ’micro’ details to the monolithic totality. The sophistication and fun–ness of the components and the simplicity and monumentally of the whole gives the building an interesting duality. In an inland city like Beijing, water becomes so precious and being with water such a luxury in people’s life. To us the Swimming Centre transcends its functionality as just an Olympic venue, it is also a paradise in Beijing’s heart that bring to people the endless happiness, joy and all kinds of fantasies of being with water.
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The juxtaposition of the seemingly soft, curved, cushiony bubbles with the sharp rectangular form of its floor plan provides another point of interest. ESD–principles The National Swimming Centre Beijing is a very sustainable building: 1. The design allows lots of natural daylight to stream into the buildings interior, which allows it to passively heat the spaces as well as the pool water. 2. The high–tech ETFE cladding system acts in the same manner as a very efficient insulated greenhouse would, absorbing solar radiation and avoiding heat loss. The double skin façade of bubbles is so well insulated that it has the potential to achieve an annual net heat gain. The principle is to capture the solar radiation in the area of the building where it is most needed around the pool and keep it there. Thermal mass of the concrete and the water will absorb and re–radiate this heat at night when it is most required. To achieve the right balance, the façade of the building has three modes of operation to respond to the climate summer, winter and mid season. The clear and translucent facades will allow high levels of natural daylight, which removes the requirement to artificially light the pool during the day. A core feature in the design of ETFE skin is the variable shading control system. By modifying the pressures in the cavity, the internal foils can be either ’open’ or ’closed’. This allows the light levels to be controlled to create a dappled effect, similar to the light under a tree or deep under water. The light can be controlled to only fall on areas that do not suffer from glaring reflections, alternatively the entire roof and wall can be turned ’off’ to achieve optimal lighting conditions for television cameras. At night the building will glow to highlight the activities within. 3. Swimming centres generally consume large amounts of water for various purposes, therefore the water cycle has also been carefully considered. Used water from the basins and showers will be recycled to reduce wastage. The grey water will then be re–used for flushing of the wc’s, any architectural water features and irrigation systems. The rain will also be collected from the roof and stored in underground tanks before being filtered and treated for re–use. Context PTW Architects aimed to design a building that was compatible in its language to the new Olympic stadium being built in the near proximity, as well as a building sensitive to its proposed urban environment, that of the junction of the axes of the Forbidden City and the Fourth Ring Road in north Beijing. We believe the National Swimming Centre should support the National Stadium. It should show wisdom and beauty without exhibiting a big gesture that competes or overpowers the National Stadium. As a counterpoint to the exciting, energy–giving, masculine, totemic image of the National Stadium, the Water Cube appears as serene, emotion–engaging, ethereal and poetic, with changing moods that directly respond to people, events and changing seasons. The sense of serenity and the potential for changing moods are considered the key features, ensuring our NSC provides that important supporting role.
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ETFE The finishing material used in the design of the building is a Teflon cladding system called the ETFE. This system was introduced to China through this project. The ETFE is lightweight and transparent. It is also a more cost effective solution that some of the more traditional materials. Because of the inherent surface properties of the ETFE, the exterior appearance of the building can be altered using different lighting and computer image projections. The Landscape around the building A cube is dropped into water; water splashes out on the earth as scattering drops with ripples spreading away. This is the theory behind the design of the landscape of National Swimming Centre. The ’water drops’ become water pounds with vegetations, sculptures, fountains or other water features. Just as the ancient square Chinese city, such as the Forbidden City, that guarded by a river, the NSC building is separated from the land around by a lineal moat at the perimeter. Bridges are the only way to lead into the building. A consistent water wall runs above the moat to lift up the space frame system from the ground. At the entrance area the water wall becomes full height with a glass curtain wall on the back to allow the ’water filtered’ day light into the lobby. People experience a walk through a water–screened space at entry every time they go into the building. Structural concept The structure of the National Swimming Centre is based on the most efficient subdivision of three–dimensional space. This pattern is extremely common in nature being the fundamental arrangement of organic cells, the crystalline structure found in minerals, and the natural formation for soap bubbles. In the late 19th Century, Lord Kelvin posed a problem: ”If we try and subdivide three dimensional space into multiple compartments, each of equal volume, what shape would they be when the subdividing surfaces are of minimum area?” This is an interesting problem, not only as a theoretical exercise, but also because such shapes are prevalent in nature. The study of soap bubbles is probably a good place to start when considering Lord Kelvin’s challenge. Plateau had already observed, in 1873, that when soap films come together, they always meet as three surfaces coming together at 120 degrees to form at edge. And these edges always meet, four to a corner, at the tetrahedral angle of approximately109.47 degrees. In 1887, Lord Kelvin proposed a solution to his own problem based on a 14 sided figure made of 8 regular hexagons and 6 squares. This figure can be constructed by cutting off the corners of a regular octahedron. However the corner angle of a square is 90 degrees and a hexagon, 120 degrees. Both of which are some distance away from Plateau’s observed ideal of 109.47 degrees. A regular pentagon has a corner angle of 108 degrees, but dodecahedra (the twelve sided figure made from regular pentagons) cannot be joined together to tile space – they leave gaps between them. It was supposed for some time that figures comprising some combination of pentagons and hexagons would be more efficient than Kelvin’s Foam. But it was not until 1993 that two Irish Professors, Weaire and Phelan constructed foam of two different cells, one of 14 sides (two hexagons and 12 pentagons) and one of 12 sides (all pentagons) that used less surface area than Kelvin’s foam.
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The Weaire–Phelan foam remains today, the optimal subdivision of three–dimensional space and we have used it as the basis of the structure for the Beijing National Swimming Centre. Despite its apparent complexity and organic form it is in fact based on a high degree of repetition. It uses only three different faces, four different edges and three different corners or nodes. So the Beijing NSC can readily be constructed using a highly repetitive, organic space frame based on one a solution of one of the world’s greatest mathematical challenges which is also common throughout nature – a social, technical and green solution. PTW Architects + CSCEC+design + ARUP National Swimming Center Beijing, China 2003–2007 Credits and Data Project title: Watercube, National Swimming Center, Beijing Client: People’s Government of Beijing Municipality, Beijing State–owned Assets Management Co., Ltd Competition management: Three Gorges International Tendering Co., Ltd. Design consortium: PTW Architects, CSCEC+design, ARUP PTW design team: Director: John Bilmon; Mark Butler, Chris Bosse, CSCEC+design team leaders: Zhao Xiaojun, Wang Min, Shang Hong ARUP: Tristram Carfrae (engineering team leader), Peter Macdonald (structure), Kenneth Ma (building services), Haico Schepers (building physics), Ken Conway (environmental), Mark Lewis (communications), Steve Pennell and Stuart Bull (3–DCAD)
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The Moet Marquee: PTW architects Chris Bosse Espace Lumiere, Space made out of Light. Introduction PTW architects designed the MOET Chandon Marquee for the Melbourne Cup 2005, the biggest annual horse racing event in Australia, together with Amanda Henderson from Gloss Creative. The Architects used latest digital technologies from concept–sketch to realization, to create a sparkling and surreal atmosphere in the name of the ”Bubble–ism”. Through the use of daylight and a tensioned Taiyo–Lycra material that is digitally patterned and custom–tailored for the space, a 10x10 ”off the shelf” marquee was transformed into a space that the press describes as an ”avant–garde environment not of this earth” Structure and Space The project renounces on the application of a structure in the traditional sense. Instead, the space is filled with a 3–dimensional lightweight–sculpture, solely based on minimal surface tension, freely stretching between wall and ceiling and floor. Building Materials Specially treated Lycra and daylight Innovation and Digital Workflow: The product shows a new way of digital workflow, enabling the generation of space out of a lightweight material in an extremely short time. The computer–model, based on the simulation of complexity in naturally evolving systems, feeds directly into a production–line of sail–making–software and digital manufacturing. Transport and Sustainability The pavilion (weight: 35 kg) is transportable in a sports–bag to any place in the world; can be assembled in less than one hour, and is fully reusable. While appearing solid, the structure is soft and flexible and creates highly unusual spaces which come to life with projection and lighting. Projects of any scale and purpose can be realized in a short amount of time. Minimal Surfaces (–any surface that has a mean curvature of zero. – for a given boundary a minimal surface cannot be changed without increasing the area of the surface–). The lightweight–fabric–construction of the pavilion follows the lines and surface–tension of soap films, stretching between ground and sky. These natural curves of bubbles are translated into an organic 3–dimensional space. Since the early seventies, with Frei Otto‘s soap–bubble experiments for the Munich Olympic Stadium, naturally evolving systems haven’t lost their fascination in the field of new building typologies and structures. Derived from Nature / Design by Optimization The shape of the pavilion is not explicitly ”designed”, it is rather the result of the most efficient subdivision of three–dimensional space, found in nature, such as organic cells, mineral crystals and the natural formation of soap bubbles . This concept was achieved with a flexible material that follows the forces of gravity, tension and growth, similar to a spider web or a coral reef.
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Light By partially letting sunlight penetrate ”through” the fabric structure, the pavilion comes to life as a ephemeral and surreal bubble experience. The perforated ceiling filters natural light and directs it onto and through the Lycra fabric, creating the depth and translucency of the space, the ephemeral quality. The light changes constantly during the day with moving clouds and changing atmospheric conditions. Credits: Project title: MOËT Marquee / Espace lumiere, Client: Moët & Chandon Australia Location: Spring racing Carnival, VRC, Melbourne, Australia Completion: November 2005 Project team: PTW Architects, Sydney, Australia Managing director: John Bilmon Associate director: Mark Butler Project architect: Chris Bosse Styling + project management: Amanda Henderson / creative director Gloss Creative, Melbourne, Australia Soft furnishings: Cameron Comer / Comer & King, Melbourne, Australia Image and concept graphics: Round, Melbourne, Australia Membrane, engineering and patterning: Taiyo Membrane Corporation, a division of the Taiyo Kogyo Group Photography: Dianna Snape and others.
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Structural Design and Optimisation of the Beijing National Aquatics Centre
M.A. Arkinstall & T.G.A. Carfrae Arup, Sydney, NSW, Australia
INTRODUCTION In 2003, as part of Beijing’s preparation for the 2008 Beijing Olympic Games, a competition was held to select an architectural design concept and structural solution for an international standard swimming centre. The competition was won by the ”Water Cube Consortium”, lead by CSCEC, with PTW and Arup providing all architectural and engineering services. The winning architectural concept consisted of a 177m x 177m x 30m regular box–shaped building filled with ”soap bubbles” or ”organic cells”. The structural engineering solution was to support the building by arranging structural members at the boundaries of each ”bubble”, and hence form a complex three–dimensional Vierendeel superstructure. The creation of the bubble concept was based on a desire for an organic looking building. The structural concept was based on the Wheire–Phelan foam which is currently the best solution to Lord Kelvin’s question, posed in 1889, ’’How can three–dimensional space be broken up such that the surface area between cells is minimised?” The Wheire–Phelan foam is mathematically formulated and completely repetitive. It is the cutting of the array of Wheire–Phelan foam to make the building surfaces that generates the apparent randomness.
Figure 1 View of Beijing National Aquatics Centre looking towards the main entry. The structural design of this three–dimensional Vierendeel superstructure was a challenging task. There were 22000 steel members in the superstructure that needed to be designed to resist dead, live, thermal, wind, fire, snow and earthquake loads under many different loading combinations. Computer automation and optimisation techniques were developed to realise the final design solution. The computer automation procedures included structural design, optimisation, and tender drawing creation. GENERAL DESCRIPTION The building will be used during the 2008 Beijing Olympic Games for swimming, diving, synchronised swimming and water polo. It will also be used after the Games as a large multi–functional recreation facility for the public. It is situated at the Olympic Green central area on a 6.3Ha site, 305m x 230m in dimensions. The site is located in a seismic zone.
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The main pool hall roof spans 140m x 120m with a 60m backspan on one side and a 40m backspan on one other side. The structural depth of the roof is 7.2m and all walls are 3.6m in width. All roof and wall geometry, including both location and widths, were controlled by the fundamental cell size, and a wish to maximise the distance of structural connection nodes from the internal and external façade surfaces. The structural design of this building was governed by strength considerations. For strength design a total of 190 load combinations were considered with only 37 different cross section sizes employed in the entire superstructure.
Figure 2 Section through the restaurant showing the three–dimensional Vierendeel structure. STRUCTURAL LOADING The roof structure was designed for a uniform live load of 0.3kPa. For robustness seven different extreme out of balance live load patterns were also applied to the roof. Similarly a uniform snow loading of 0.45kPa was considered, together with seven different extreme out of balance snow load patterns. These out of balance snow loads were used in conjunction with wind loads to simulate extreme snow drift conditions for various wind directions. The wind loads were derived from the Chinese wind loading code, given this building is simply a box in shape. Three levels of earthquake were considered during design, with the response spectra being derived from a site–specific hazard assessment. Structure self weight was applied as member loads, together with an additional component at each node location to account for additional connection weight. Superimposed dead load was applied as 0.15kPa for uplift cases or 0.54kPa for downward cases. LOAD PATHS The structural system used for the Water Cube is a three–dimensional Vierendeel. As such, changing any one member in the structure causes a redistribution of the forces and moments in the members surrounding it. This also means that the load paths are not statically determinate. The structure predominantly resists load by moment frame action. The main roof span, the internal and external walls, can each be imagined as a four–sided supported flat
LSAA 2007 Surfers Paradise Oct 25/26 Page 31 Lightweight Architecture Stretching Our Boundaries Internationally plate with differing moment fixity along each edge. Each plate consists of thousands of linked cells or bubbles, without triangulation, that transfer load to adjacent cells via bending action. The top and bottom surface of the roof does attract some axial load in a way similar to a truss with a soft web. There is a large amount of redundancy and ductility in this structure which makes it ideal for energy dissipation in this seismic region. CROSS SECTION SELECTION The superstructure was grouped into three types of structural element for strength design. The surface edge members were one such group. Their cross section size was architecturally governed as 300 x 300 RHS sections. Only the wall thicknesses of these members changed, with 8 cross section options in total. The internal and external surface members, excluding edge members, form the second group. These vary in cross section from 450 x 300 RHS to 180 x 300 RHS sections, with 13 different cross section options for this group, including geometric and plate thickness changes. The final group of members are the internal ”web” members. This group consisted of 16 CHS cross sections varying from 219mm diameter to 610mm diameter. The maximum plate thickness used anywhere in the design was 40mm while the minimum plate thickness was 4mm. All steel was specified as grade Q345 which is equivalent to grade 350.
Figure 3 Grouping of structural members for cross section allocation and strength design. Every member in the superstructure was allocated to one of the three groups above. Each group was then allocated a number of different cross section sizes, specific to that group. Any single structural member in a particular group could potentially be any one of the cross section choices allocated to its group.
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DETERMINING CROSS SECTION CHOICES FOR EACH GROUP For each of the groups, an optimised set of cross section choices needed to be derived, which would be employed in a global optimisation. As the overall design was governed by strength considerations, local cross section strength per kg of steel was maximised for each cross section considered in each group. The cross section choices in a group gradually increased in stiffness from one section to the next, without large jumps between adjacent similar sizes. The gradual stiffness change from one section to the next was crucial for the global optimisation procedure to be effective. INVESTIGATION OF STIFFENED CROSS SECTIONS VERSUS COMPACT CROSS SECTIONS During the design process the use of stiffened cross sections to reduce steel tonnage was investigated. The key issue here was the structural performance of stiffened cross sections during the rare event earthquake, which would load the stiffened cross section plastically. One of the most important factors when designing a long span roof is the self–weight behaviour, which can significantly reduce available strength to resist other loads. It was hoped that by using stiffened cross sections, the steel tonnage would be reduced, resulting in reduced member forces and seismic mass, which would in turn lead to further reduced cross sections sizes. This would then lead to further reductions in member forces, and so on, until an optimum lighter solution was achieved. However, it was shown by elastic, inelastic, and plastic finite strip buckling methods that plastically loaded stiffened cross sections buckled before a satisfactory level of ductility could be achieved. As the stiffeners could not be relied upon under plastic loading, the structure had to be designed to resist the rare event earthquake elastically. This lead to an increase in the structural steel tonnage. Inelastic buckling is buckling up to first yield. It does not track buckling beyond yield. In terms of most design standards, a section that can buckle inelastically at the yield stress would be at least non–compact. However, to classify a section as compact there needs to be a certain amount of stable behaviour beyond yield into the plastic range. For this to be assessed the section needs to be pushed into the plastic range. So inelastic buckling is only valid up to first yield (and can be similar to elastic buckling if the buckling stress is well below yield), while plastic buckling allows us to look beyond first yield into the buckling behaviour of plastically loaded sections.
Figure 4 (a) Elastic buckled shape under pure compression; (b) Inelastic buckled shape under pure compression; (c) Plastic buckled shape under pure compression. The graph in Figure 5 shows the variation of critical buckling stress as the length of cross section buckle is increased out of the page for the cross section shown above in Figure 4. The maximum strain of the cross section at the point of plastic buckling versus buckling length is also plotted on the right hand vertical axis of Figure 5. The elastic critical buckling stress was above the yield stress and so not relevant for design. The inelastic buckling analysis
LSAA 2007 Surfers Paradise Oct 25/26 Page 33 Lightweight Architecture Stretching Our Boundaries Internationally employed an inelastic Winter plate strength curve together with Ramberg–Osgood material parameters to show that the cross section remained fully effective up to the point of Euler buckling; ie, the inelastic critical buckling stress was equal to the yield stress up to the point of Euler buckling. This is equivalent to a non–compact classification in AS4100–1998. The plastic finite strip buckling analysis results show that the plastic buckling strain was equal to the strain at first yield, except for very small buckling lengths and beyond the point at which Euler buckling governs. This confirmed the results of the inelastic buckling analysis, and also showed us that the stiffeners would not provide the necessary ductility to resist the Level 3 seismic event. The construction of such a sophisticated structure would inevitably result in locked–in stresses and the use of stiffened cross sections would increase fabrication cost and connection complexity. For these reasons, together with the lack of available ductility for stiffened cross section loaded plastically, all cross sections adopted in the final design solution were unstiffened cross sections and they comply with the requirements of a compact section to the Chinese design codes.
Figure 5 Variation of critical buckling stress and plastic buckling strain with buckling length for elastic, inelastic and plastic finite strip buckling analysis of cross section in Figure 4.
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AUTOMATED GLOBAL STRUCTURAL ANALYSIS, DESIGN AND OPTIMISATION OF THE WATERCUBE SUPERSTRUCTURE The Water Cube superstructure consists of 22000 structural members that each need to satisfy the strength requirements of 11 different Chinese steel design code clauses at 5 points on each member for 190 different load combinations. This equates to 230 million design constraints needing to be satisfied by varying 22000 discrete variables in a strength optimisation to minimise overall steel tonnage. This problem is too large for gradient–based optimisation methods, probabilistic optimisation methods or genetic algorithms and so an alternative method was needed to arrive at a final satisfactory design. The method adopted was a constraint satisfaction method. Strictly speaking this is not optimisation to the purists, however it did result in a significantly lower steel tonnage via an iterative converging process while satisfying all of the design constraints. The automated analysis/design/optimisation process is outlined in Figure 6.
Figure 6 Flow diagram of Analysis/Design/Optimisation procedure.
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The optimisation process commenced with each member in the superstructure being set to the minimum strength cross section for its group. A structural analysis was then performed using the Strand7 structural FEA software before the member forces were extracted and strength design checking performed for every member under every load combination. At the conclusion of an iteration, members that were over–utilised were increased in size while members that were under–utilised were reduced in size. Due to the sensitive nature of the structural system, member size increments were limited to one size increment per iteration to control the amount of force redistribution that would occur as a result of stiffness distribution changes. It is for these reasons that the determination of the optimum cross section choices for each of the three member groups was important, as it affects the convergence and result of the global optimisation process. Figure 7 shows the distribution of cross section sizes before and after optimisation.
Figure 7 Structure member sizes by colour; (a) before optimisation, (b) after optimisation.
The structural analysis, Chinese design code strength checks, modification of member cross sections after an iteration and creation of a Microsoft Access calculations database described in Figure 6 were all controlled by computer software specifically written for this project using Visual Basic programming. In particular the software developed interfaced directly with Strand7 using its Application Programming Interface (API). This allowed data in the Strand7 analysis model such as the beam element properties to be modified directly, and all analysis solver options to be set and the solver executed directly from the Visual Basic application. Similarly, member forces and moments were extracted directly from the Strand7 results database using API function calls. All strength check results, utilisations, and member stresses were written directly to the MS Access database upon convergence of solution.
There were several key aspects of the design that needed to be built into the automation software. Firstly there was a need to build in upper and lower strength utilisation limits for every cross section choice in all three groups. If a structural member were strength–utilised below its lower strength utilisation limit then it would need to be reduced in size. Likewise if a member were strength–utilised above its upper strength utilisation limit then it would need to be increased in size. A further option developed was the ability for all members of the same cross section size to be moved up or down in size together based on the critical member utilisation for the those members. This allowed different sub–grouping patterns to be investigated to try and rationalise the structure’s member sizes into geometrically defined regions. Unfortunately for these investigations no valid solution could be found. Full optimisation of every individual member was required to achieve a valid solution.
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The seismic ductility force reduction factors for different seismic cases also needed to be controlled. Built into the automation software was the ability to define independent groups solely for the purpose of allocating different seismic ductility. For final design all seismic ductility groups were set to be the same as the cross section groupings. Each seismic ductility group was allocated an R (seismic ductility force reduction) factor for every load combination by which the seismic forces could be divided to obtain design moments and forces. For non–seismic load combinations R=1. For the Level 1 and 2 earthquakes R was also set to 1. However for the rare event Level 3 earthquake, R=3 was adopted for the compact cross sections. During the optimisation process an equivalent static earthquake load case was applied to expedite the optimisation process for all three earthquake levels. On final convergence a full response spectrum analysis including the substructure was performed in Strand7. Mass participation of at least 90% was achieved in both lateral directions and for the roof itself vertically, with 4424 natural modes included in the solution. The structure was re–assessed for strength based on the results of the response spectrum analysis. A non–linear static pushover analysis was also carried out using Arup’s own material and geometric non–linear static dynamic relaxation solver, GSA. Due to the large redundancy in this structure, the use of compact cross sections and the numerous possible plastic hinge formation locations, the structure was shown to comfortably withstand the Level 3 earthquake within reasonable plastic strain limits.
Figure 8 Convergence of global structural optimisation process.
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The convergence on a solution occurred rapidly with only 25 iterations required for the final tender design. A complete structural analysis was performed after each iteration due to significant stiffness changes as a result of under–utilised and over–utilised members changing cross section size. Figure 8 shows the convergence of the solution in terms of number of overstressed members per iteration and total steel tonnage per iteration. It was found that different starting assumptions on initial member sizes resulted in different final solutions, with the minimum steel tonnage being achieved by starting at the minimum cross section for all beams. This is not surprising considering how crucial self–weight of structure is in the design of long span roof structures. It was also found that the more continuous the discrete cross section choices for a group were, the more rapidly the solution converged and the lower the steel tonnage. The upper and lower limits of strength utilisation set for each group also had an impact on the final tonnage. It was found that setting both the upper and lower limits as high as possible resulted in the lowest tonnage. Of course if the lower limit is set too high compared to the upper limit, elements could flip–flop between under– and over–utilised, resulting in non–convergence. As locked–in residual stresses from construction will occur, the superstructure was optimised to achieve 80% strength utilisation, leaving 20% utilisation for construction stresses. Figure 9 shows the final strength utilisations contoured on the superstructure while Figure 10 shows the distribution of strength utilisations for the entire structure.
Figure 9 Contour plot of strength utilization for each structural member after optimization.
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Figure 10 Histogram showing the number of members in each 10% strength utilization band after optimisation. EARTHQUAKE RESPONSE SPECTRUM ANALYSIS The structural optimisation and design process assumed a first mode cantilever response to earthquake loads. To apply this simplified loading, a percentage of gravity load was applied laterally with a base shear as calculated by a hand method to the Chinese seismic code for the Level 1, 2, and 3 earthquake events. For the Level 1 and 2 earthquakes the structure was designed to remain elastic with no seismic ductility force reduction used. However, for the rare event Level 3 earthquake a seismic ductility force reduction factor of 3 was employed. The severity of the Level 3 earthquake was one of the main reasons why compact cross sections were used in the final design. The Level 1, 2 and 3 site specific response spectra can be seen in Figure 11. The seismic ductility force reduction factors were incorporated into the automated optimisation process by allowing the creation of subsets of structural members with differing ductility force reduction factors for every load combination.
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Figure 11 Site–specific Response Spectra for the Water Cube site.
Figure 12 First four natural modes of the optimised structure. The first four modes of the optimised structure are shown above in Figure 12. Modes 2 and 3 show a similar mode shape to that assumed for earthquake in the optimisation process. However, they only contribute a relatively small amount of mass participation, as seen in Figure 13, while a minimum of 90% mass participation is required by the Chinese seimic design code for response spectrum analysis results to be acceptable. To achieve this 90% mass participation, a total of 4424 natural modes had to be computed. This was a challenge in itself. The solution of a 22000 beam element, 3000 shell element structural analysis model for 4424 natural modes was achieved by solving for small batches of about 30 modes at a time and then
Page 40 LSAA 2007 Surfers Paradise Oct 25/26 Lightweight Architecture Stretching Our Boundaries Internationally overlapping each consecutive batch. As each batch of modes was found, an upward frequency shift was set for the next batch. Only unique modes from each new batch were stored and after each batch the cumulative mass participation was recalculated. Once the 90% mass participation was achieved, the modal solution was complete, and all unique modes from each batch were assembled into a single set of natural frequency mode results that could be employed in a response spectrum analysis. This process was automated by a Visual Basic script specifically written to interface seamlessly with the Strand7 analysis software using its API. An advantage of this method of solution was that computer RAM and hard disk requirements were kept to a minimum. This batch procedure was more efficient than the solution of all the modes in a single run. The mass participation for each mode together with the cumulative mass participation for all 4424 modes are shown in Figures 13 and 14 respectively. It is clear that this is a special structure in terms of its dynamic properties and modal response. It is worth noting that the vertical (Z) cumulative mass participation appears to be only approximately 60%. This is based on the total structural mass. If just the roof mass is calculated, then the vertical cumulative mass participation for roof modes is in excess of 95% mass participation.
Figure 13 Mass participation of each natural mode of the structure.
Figure 14 Cumulative mass participation for all natural modes up to 90% mass participation.
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A response spectrum analysis was then performed for each of the Level 1, 2, and 3, earthquakes and the final pass strength checks performed on the Water Cube structure using the optimisation software in design check mode, for the more refined earthquake forces. CONCLUDING REMARKS The novel three–dimensional Vierendeel structural form, based on the Wheire–Phelan foam, of the Beijing National Aquatics Centre is a world first for building engineering. The structural design was an extremely complex and sophisticated piece of engineering, made possible only by the use of the finest computer and software technologies of today. The automated analysis/design/optimisation computer software developed has since been used on other significant projects in China with great success and will continue to be used on future projects. CREDITS 1. CAD model images created by Arup+PTW+CSCEC.
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Austrade’s Global Network – how to use it and the value it can bring to your business
Jeff Turner National Manager, Infrastructure and Major Projects, Austrade
Jeff Turner is the National Manager, Infrastructure and Major Projects, Austrade. Previously he was Executive Director of the Australian Business Centre in Taipei. Prior to taking up that position in early 2004 Jeff was Trade Commissioner in Ho Chi Minh City, Vietnam for 3 years. From 1997 to 2001 Jeff was Trade Commissioner in Taipei. Jeff joined Austrade in 1995 and was in charge of the China desk in Canberra. Before joining Austrade Jeff ran his own consulting firm specialising in providing advice to Australian companies doing business in Asia, especially in China as well as offering translating and interpreting services, specialising in Mandarin Chinese. Jeff developed his Asia business skills on the ground, having studied and worked in China, with 3 years in Shanghai and 4 years in Beijing as Chief Representative for Stephen FitzGerald & Co. He has broad industry experience having worked with companies in mining, building and construction, agribusiness, consumer products, ICT, education and training, biotech and environmental technologies.
Jeff has a Bachelor of Economics from ANU and a Diploma of Asian studies from Fu Dan University (Shanghai, China). He is fluent in Mandrin Chinese and proficient in Vietnamese.
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Techniques and Solutions to Installation of Tensile Membrane Fabrics
Dean Peters Ozrig
I would like to talk to you all about a number of issues relating to the installation of large membrane structures and the techniques and solutions to overcoming some of the issues that can be encountered. I will be dealing directly with the techniques of handling deploying and tensioning various large fabrics and some solutions for dealing with difficult issues on site in the installation of these projects. Briefly as most if not all of you know there are so many different products and variations of product on the market these days. Each of all of these products require different consideration with regard to: H Stretch criteria and compensations –creep H Fabric compositions and versatility and stretch compensations – PVC, Mesh H Application requirement/suitability – Fire Retardancy H Ease of manufacture and freight i.e. Fibreglass fabrics require padding between folds H Handling and installation requirements/issues traffic ability For example the basic types of fabrics, PTFE (Fibreglass fabric), PVC (Vinyl) and Shade mesh are similar in effecting various shade solutions. Although require different handling, deploying methods, hoisting and tensioning during the installation process. At this point one thing I must stress is that from an installation perspective each member of a project from planning and design to construction personnel and engineers has a part to play in enabling the erection crew to complete their installation quickly and efficiently. Depending on what particular type of fabric structure or tensioned membrane you are building there is always at least one if not a number of issues that can offer a challenge. These include: H Logistical issues Height restriction including proximity of steel to fabric beneath and above the structure. Elevated heights, working and trafficking steel and fabric. Elevated work platforms: usable/unusable. Deployment of fabric at height: no crane/no boom lifts. Accessing all points at heights: no boom lifts. Using rope access or scaffold.
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H Structural/Design issues Rigidity of steel frame structure: Need for temp Tensioning into blind corners. Practicality of steel design for installation Complexity of steel componentry and connections Environmental Issues Wind, rain, heat/cold The important thing to remember is where there’s a will there’s a way. And once again to reiterate the basic resolve to all these issues is a little pre–planning and discussion on the criteria of each job to eliminate any and all fore seeable hazards and construction hiccups that might occur. Obviously to cover every issue that relates to construction process and the solutions to overcome these issues would take some time – more time than I have right now, and definitely more material than I have with me. So I have just picked out a few of Ozrig’s recently installed projects and I would like to just briefly show these to you and provide a bit of a visual on how we get some things done. Firstly when deploying fabric onto steel frame it’s not always possible to have a flat area adjacent to the structure to lay out a fabric or lift a fabric from, even the use of cranes is not an option. In many cases fabric in its loose state is vulnerable to the elements. Particularly wind and rain and so the use of webbing is employed. This picture shows deploying fabrics from roof level between steel frames on top of a webbing platform Ozrig installed. Webbing The use of a webbing type platform facilitates deployment and control of an entire structure or panel of a structure. In some cases webbing can be setup to sandwich the fabric the entire time it is being deployed top and bottom and sliding the panel through. In either case securing ropes or webbing should be deployed with the fabric simultaneously and secured as soon as possible once the fabric has been deployed and before tensioning. Another type of platform can double as a lifting rig Steel framed platforms are often fixed to steel elements on a structure for the purpose of deploying fabrics. These platforms have to be engineered and certified for traffic ability, load rating capacity and so on. Theses platforms are re usable and allow fabrics to be deployed at heights with precise placement and control of the fabric. Obviously the actual pulling out of the fabric is done by hand or with cable Tirfors or chain motors. Platforms – Purpose built deployment platforms Fabric is positioned and rigged up on the platform ready for deployment once in situ. Then lifted to steel super structure And bolted off and secured Scaffolding built into a platform is a last resort option for deploying fabric are very effective and functional, however they are extremely costly. As I mentioned pulling out fabric is usually done by hand with ropes, tirfors or chain motors. Another means of spreading the fabric is through the use of:
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Spreader Bars H Purpose built or bolt together steel trusses of various lengths H We recently used a spreader bar in Melbourne that we bolted together on site. Its length was 39 metres this allowed us to position the fabric on a webbing net on top of a steel frame which was then deployed with Tirfors. H The only downside being the size of crane that you need to use for such a spreader in this case it was a 160 tonne crane. This then leads to the question of access to the structures at heights. Access There are several methods of accessing difficult areas
1. EWPS and Boom lifts Any mans preferred option as a means of access allowing close working proximity to the task with a safe and stable platform to heights in excess of 30 metres.
MSAC PHOTO
2. Scaffolding
Here is a purpose built scaffold used to access this difficult area and to close the field joint and tension the mast and fabric
3. Dog box
You can see in these photos purpose built scaffold to access all edges for tensioning and deploying purposes.
4. Twin ropes Accessing some locations will demand a bit of old fashioned hard yakka via twin ropes access or trafficking the fabric.
Accessing Bale rings Closure flaps being welded on a PTFE cone. This photo shows a crew welding closure flaps over a field joint between two fabrics. This photo shows a crew almost a panel replacement on a PTFE structure. The circumstances of the task will always dictate what method of access is required in any situation. It is important to remember that life lines should be employed when working at heights from steel super structures or roofs and gutter sections. Once you have access to work areas and have deployed the fabric then you will need to tension the fabric, cables and associated hardware. Some of the most common and useful manual aids are: Aids to the installation process: H Rope edge clamps Sheave blocks H Split sail track Corkscrew clamps H Chain pullers Double sided rope edged track
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H Wire rope pullers Hydraulic jacking rams H Tirfor blocks Nylon slings and high stretch ropes H Tensioning (Clamps – Chain blocks) A combination of soft slings shackles and clamps and pullers can be used singly or in gangs to tension individual points or entire lengths of a structure. As in the picture a fibreglass fabric is being tensioned to make connections. This picture shows tensioning a field joint with threaded rod and fitting fabric under tension to membrane plate. This shot also shows fabric joint tensioning and next two pictures Hydraulics Another type of tensioner is the hydraulic pump and ram. These are used to tension masts with attached bale rings which are controlled with guy cables. Design tension is reached through hydraulic jacking. Tensioning with Wire rope pullers If ever there is a case to pull flexible steel wire rope or cable then the use of wire rope pullers are a very inventive but practical tool designed to be able to latch onto steel or stainless cables to pull wire cable to make connections. This is not recommended for tensioning to achieving design loads. connections. And so in closing, in attempt to try to take up as little of your time as possible and without giving away too many secrets. I leave you with a few images of a structure Ozrig recently disassembled. which will answer your questions as to how this should be done also.
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Kuwait Airport VIP canopy
I A Norrie VDM Consulting Engineers
Summary: The Kuwait Airport VIP canopy is a cable supported steel and fabric roof, 35m high, spanning 120m, with 5350m2 of PTFC fabric and 265t of steel.
It forms the official arrival canopy for VIP guests arriving at Kuwait International Airport.
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SILICONE COATED ARCHITECTURAL TEXTILES
Johann Müller, Wacker Chemie GmbH, Burghausen
Presented by James Dar Sila Australia
Silicone coated technical textiles are well established in many application fields. In many cases silicone coating opened completely new application possibilities. In the last century, silicone coatings have shown a really fast growing development. Airbags, conveyor belts, protective clothing, hospital textiles, high performance clothing and Para gliders would not be possible without the benefits conveyed by silicone coatings. Can these special properties of silicone coatings also be used for architectural textiles, such as awnings, black out curtains, or even membranes for large roof constructions? In this lecture we will try to answer this question. Properties of Silicone Rubber Let us briefly look at silicone chemistry. Silicone rubber consists mainly of dimethyl polysiloxane units with reactive groups. Reinforcing fillers and different additives are added to influence to the final mechanical properties.
When applied to a surface the silicone rubber orients itself according the polarity of the substrate surface. The non polar, non reactive methyl groups tend to move away from the surface.
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This is the reason for the typical surface characteristics of silicone rubber coatings. H Low surface energy (22 mJ/m2) H Hydrophobicity (Contact angle > 100 degrees) H Dirt repellence H Self cleaning with rain In combination with the well know properties of silicone rubber such as H Temperature resistance from – 50 to + 200 degrees C H Flame retardancy H Durable elasticity H Transparent or readily pigmented H Resistant to weathering and ageing H Resistant to many chemicals H Free of halogens H Ease of use you can see why Silicone Rubber is a nearly ideal coating material for architectural textiles, both for interior and exterior applications. When pedestrian areas, sports stadiums or official buildings – that means big projects – are covered with a membrane, it is important that as much as possible of the visible light should pass through the membrane. The transmission spectra of a silicone coated glass fabric shows that exactly this requirement can be met by a silicone rubber coating. And there is an additional benefit: UV–B and UV–C radiation, which is harmful for plants, animals and humans, is largely blocked by the silicone coating but the UV–A radiation, necessary for plant growth, is transmitted.
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Welding Silicone rubber is not thermoplastic unlike, for example, PVC. Thermal welding or high frequency welding is not possible. Fast and durable gluing with silicone adhesives is, however, well established. Room temperature curing 1 – component silicone glues or 2 – component, heat curing silicone adhesives are well known from the past. Recently a silicone adhesive tape has been developed. It can be applied from a roll directly to the silicone coated fabric. It cures under heat and pressure. Well known press bars can be used to achieve reliable bonding of the fabrics. Curing temperature can be from 150 to 200 degrees C. Dependant on temperature, the curing time is from 20 to 60 seconds.
Peel forces up to 400 N/5 cm according DIN 53 530 can be reached.
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Comparison of Different Membranes
Silicone coated fabrics are very well suitable for all architectural applications. For interior applications, for example, awnings, black out curtains, wall coverings and sound protection, and exterior applications such as membranes for air supported constructions, big tents and various kinds of roof, silicone coated fabrics have been used very successfully.
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Black out curtain
Expo 2002 Biel
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Expo 2002 Biel
SILICONE RUBBER – A HIGH TECH MATERIAL FOR INNOVATIVE APPLICATIONS
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Construction of Local and International Projects using EFTE
Ben Morris, Angus Macleod and James Murphy Vector Foiltec
Introduction: In 2001, the Eden Project in England was the largest ETFE structure in the world comprising 30,000sqm of Texlon ETFE pneumatic cushions. Due for opening in 2008, the Beijing National Aquatic Centre incorporates over 100,000 sqm of Texlon ETFE and therefore formalises the technology as one of the most versatile ’new’ construction technologies available. Background: The use of pneumatic cushions as a roofing or cladding material first hit the public stage at the 1970 World Expo in Osaka Japan where several large spaceframes were clad in pneumatic cushions made from Polyester. However for various reasons, the system never really established itself as a viable technology. The origins of ETFE in construction date back to the early 1980’s when a small group of sailing enthusiasts were looking for alternative materials to make sails out of. ETFE was one of the materials assessed and quickly rejected because of its material properties. However, the group realised that the same properties that made it unsuitable for yacht sails made it ideal for use in the building construction industry but only when used in a certain fashion. From these humble beginnings the Vector Foiltec group was founded. Today, Vector Foiltec have completed over 500 projects in more than 30 countries – more than 95% of all the ETFE structures in the world. Vector Foiltec are the world’s largest ETFE specialist contractor and have been responsible for obtaining local authority approvals for the technology in every country that ETFE has been utilised. Why ETFE? ETFE is quite a peculiar material to work with as it has specific properties which, if they are not respected and the implications analysed can lead to disastrous results. Experience therefore plays a large part in building with ETFE. However, some of the key benefits of the technology include: H Longevity – lifespan in excess of 25 years H Inert – does not react with acids, alkalis, solvents etc H Low skin friction – similar to PTFE but since it is an extruded material is also ultra–smooth H Excellent thermal properties H Cost competitive when compared to other solutions The last item is an interesting one for the LSAA forum as we generally do not count ourselves as ’lightweight structures’. The main reason being that Texlon ETFE pneumatic cushions are a panelised system as opposed to a tensioned membrane – we are therefore more often compared to glazing than to fabric structures.
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Beijing National Aquatic Centre: The design brief required the building to be a world class leading building that achieves the theme of Beijing Olympic Games – Green Games, High–tech Games and Peoples games. The project itself represented a massive undertaking for the company. The scheme called for approximately 100,000sqm of some of the largest Texlon ETFE pneumatic cushions ever attempted. To do this, new ways of making the cushions had to be invented as well as figuring ways to strengthen the cushions to achieve the spans & loads required. Technical limitations in the material production led to multi–layer cushion configurations previously only used on a handful of projects and never on this scale. To give some idea, the total tonnage of raw ETFE material used for this project was 90 tonnes – in 2005 when we were awarded the project, the global production of ETFE resin suitable for architectural use was only 100 tonnes. Since then of course, supply has increased significantly! Shortly after being awarded the contract, Vector Foiltec were then notified that the base structure was changing to a fully site welded frame from a bolted scheme that was originally envisaged by Arup Engineers. This represented a major issue as the programme would not allow site measurements of steelwork followed by overseas fabrication and transit times. Site measurement was deemed critical to give the wrinkle–free appearance. The erection of the steelwork was also an extreme feat of engineering. Being completely site welded, at times there were up to 2,000 welders on site even during the depths of a Beijing winter. One can only imagine the amount of power required to pre–heat the steelwork for 2,000 welders in –10 deg C weather. The entire steel structure was erected using a birdcage scaffold system which will surely be included in the next Guiness Book of Records! In response to all of these challenges and other logistical concerns, Vector Foiltec opened a purpose built ETFE cushion fabrication facility in Beijing in 2006. Here we manufactured purpose built machines capable of not only generating the cushion sizes required for the project but also maintaining the strict quality control required for long term cushion viability. The facility was also designed so that site measurements for the cushions could also be taken off the base site steelwork and incorporated directly into the cushion manufacturing parameters to ensure a good and wrinkle free fit. Another key technical challenge faced by Vector Foiltec was the use of a flat roof on the project. One of the material characteristics of ETFE is that it has up to 400% elongation at break. One of the defining design criteria of an ETFE system is that a cushion must not be allowed to fill with water or snow during deflation. As a deflated cushion fills with water, the material would stretch – thereby making the cushion deeper and able to accommodate more water until eventual failure. Therefore the trick is to not allow this eventuality to occur in the first place – either through risk management associated with the air supply or by other means. This problem was eventually solved by several methods including inflation unit redundancy, backup power systems and locally reinforcing critical areas. Installation on the site was another challenge. It was originally envisaged that teams of rope access installers would abseil down the facades to install the technology – this is our standard installation technique. However, while refining the design we realised that in China site labour is not the cost center that it is in other cultures. Our standard details try and be as efficient as possible with regard to site labour. For this project, labour was not a key issue and so the details and work practices could be revised accordingly. Three methods of training for installation teams and methods of installation were developed specifically for China :
1. Horizontal cushions were installed from the main steel structure. Debris nets were installed to allow work to continue below.
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2. Exterior vertical cushions were installed using a custom made platform
3. Interior vertical walls cushions were installed using lightweight scaffold. At the peak of installation we achieved an installed rate 2500m2 per day. Steel and other trades could not provide sufficient work areas for a continuous work flow. It was therefore critical for the Head Contractor to involve the ETFE contractor in the development of sequence of installation and minimum work areas. There are several methods by which the ETFE subcontractor can accelerate the schedule including the use of innovative construction methods that do not require birdcage scaffolding. Summary: Overall, this project is one Vector Foiltec have been proud to be associated with. We applaud both the vision of the Architects and the courageousness of the client to build what will undoubtedly be one of the most outstanding pieces of Architecture in the world for many years to come. Facts: 1. Total ETFE façade area 102,000 m2
2. Building footprint – 177.77m x 177.77m
3. External wall height 33m
4. Custom Silver print was applied to the foils to reduce solar heat gain
5. Prints pattern densities were tuned to the activities for internal spaces; more light/solar energy allowed into the building at circulation areas, less light/solar energy allowed entering building at competition hall.
6. All external foils are blue.
7. Double wall façade and roof.
8. External roof cushions use four layers of ETFE to create three air chambers.
9. Internal ceiling cushions use four layers of ETFE to create three air chambers.
10. External facades walls use three layers of ETFE to create two air chambers.
11. Internal perimeter facades walls use three layers of ETFE to create two air chambers.
12. Internal walls use two layers of ETFE foils to create one air chamber.
13. Three internal rooms are created using double walls of ETFE cushions.
14. Volumes of air enclosed in the building weigh more than the building.
15. ETFE double wall system reduced plant equipment sizes by 40%.
16. Approximately 1million cubic meters of handled air.
17. Design temperatures external –12 degrees Celsius internal temperature +33 degrees Celsius.
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18. Observed temperature in the ceiling cavity reached 44 degrees Celsius during construction.
19. Cavity acts as insulator .
20. Maximum Structural span 110m.
Owner: Beijing State Owned Assets management Co., Ltd. Design Consortium: Lead of the design consortium: China State Construction Engineering Corporation China State Design International PTW Architects Arup Sydney Design and Build façade consultant and contractor Vector Foiltec General Contractor: China State Construction Engineering Corporation Summary
Various aspects of the construction of the EFTE component of the Beijing Watercube and other projects are discussed by means of the following slides.
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Update on Fire Testing for Tension Structure Fabrics in Australia, (and overseas developments)
Brian O’Flaherty Indtex Australia Pty Ltd
Background This is an interesting journey into Government regulation, and how hard it is to get changes to Australian Standards. The perspective is that of a fabric supplier. BCA The Building Code of Australia calls up AS1530/parts 2&3 in the regulation of fire performance for tension membrane fabrics. Specifically Class 2–9 Buildings Specification C1.1, Clause C1.10. There is an anomaly in the BCA in that there is no specific category for tension membrane or tent/marquee roofing materials and generally these structures have historically been put into the sub–section ’sarking’ or ’other’. (It is time, in fact well overdue, that membrane roofing materials had their own sub–section and was not just lumped into ’sarking’ or ’other’). The BCA only makes reference to the ’Spread of Flame Index’ and the ’Smoke Developed Index’. For the purpose of this paper there is no need to go into further detail on the actual test, suffice to say that the test AS1530 nominated in the BCA was probably never applicable in the testing of fabrics, in particular thermoplastics like PVC which are the workhorse of the industry. Temporary structures such as tents and marquees are regulated at State level, having requirements which are based on AS1530. (This also needs addressing, a separate sub–section in the BCA is long overdue). AS1530 –The Test AS1530 was developed from corner–wall burn experiments to grade cellulosic wallboards according to their tendencies to ignite and spread flame vertically. Over the intervening years this test had also been modified to include a smoke test, and AS1530 was utilized over the years for an expanding list of building materials. I understand that it is not unusual for a test to be adopted and used in areas it was not originally designed for, many other countries have similar experiences. Whilst AS1530 was not an ideal test for tension fabrics most suppliers (PVC manufacturers in particular) had learned how to manage the conflicting requirements of a low spread of flame result whilst limiting smoke (made difficult as the chemicals used in the PVC fabrics to extinguish the flame showed up as smoke on the optical testing mechanism). Problems Arise By the mid 90’s however it was becoming clear, to suppliers at least, that something was amiss with the test. The AWTA had changed the validity of its test certificates to 2 years which lead to suppliers getting frequent requests to update their certificates. When they did this they were finding vast differences from the original results, so much so that they were no longer able to meet the BCA requirements. This was very suspicious as in a lot of cases had been no changes whatsoever in the formulation.
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We made our initial enquiries with the testing houses, AWTA, but this produced nothing, however at subsequent discussions with the CSIRO Fire Research Laboratories, it became immediately obvious what the problem was. The CSIRO knew immediately what the problem was, the test method had in fact been changed in 1999. Subtle changes in the method of clamping the sample had had a marked effect on the results, particularly thermoplastic materials. A search showed in fact that these warnings were clearly documented in the literature! Action It began as quite a lonely ’crusade’ by us. CSIRO was certainly very aware of the problem, the BCA seemed aware of the problem but said they had no plans to go forward, in fact they were addressing it for ’sarking’ materials and a report had been prepared in 1998 on replacement tests for wall and ceiling linings, however it seems that membrane roofing materials were overlooked in this review. The new proposed test (Cone Calorimeter) for linings was not appropriate for the thicker materials used in roofing membranes. Despite repeated requests from us, and now other suppliers and from the two Industry Associations LSAA and ACASPA, (that had been getting a growing chorus of member frustrations), there seemed to be no movement whatsoever in Canberra. Stalemate A stalemate had developed. With no possibility of re–testing fabrics (hugely expensive full scale tests for individual projects were out of the question) old certificates were being allowed in some constituencies but not in others, fire engineers had to be brought in on some projects, and there was general confusion in the community. An altogether unsatisfactory situation. White Knight 2006 enter John Shaw of The Victorian Building Commission. The BCC was responsible for the licensing of temporary structures in Victoria. We had brought the problem to their attention in 2002 and although BCA changes were outside of his responsibility John was now experiencing the problems first hand. John decided to sort the mess out himself for the Victorian temporary structures industry and arranged a meeting of interested parties (incl; CFA, MFB, fabric suppliers, tent & hire industry, engineers). Since the same test method would most likely be needed in the tension membrane industry this was to be borne in mind by the committee, ultimately with the aim of incorporating this test is the BCA. It is my understanding that John has the blessing of the other States to take the lead in this matter. Warrington Fire Research was employed by BCC to give technical assistance to the Committee. Two meetings have now been held and as a result a Draft proposal presented by Warrington. Unfortunately at this stage we are not all in agreement on the direction and it may take some further work to move on. The test method being proposed by Warrington is a modification of ISO9705, and even in its modified state is a factor of ten times more expensive than the old AS1530! Warrington position is that this is the only test that meets all the criteria set down.
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Fabric Suppliers Position The ISO9705 test, even in its modified form, is too costly, a small scale test is required. If this test method is adopted it is going to have serious effects on the industry that will restrict in particular any new fabrics, or new suppliers to the industry. At this time there are two or three major suppliers of fabrics to this industry, with a handful of established products. Clearly those products will have to be tested as these suppliers have sufficient market share to justify it. What of the other less entrenched and smaller suppliers, are they going to spend $10,000 to test a fabric in the hope of selling it. Experience says not, they will try for an order first, however the purchaser is going to be very reluctant to order without all the certification in place. The same applies to newly developed products from the current existing suppliers. As it stands the larger companies are prepared to outlay $1,000/test (with no guarantee it must be said that it will pass first time, it may need to go back for re–formulation and re–test more than once, at $1,000 a time) and then put the product into store in the hope of selling it. Clearly at a cost of $10,000/test this will be a significant barrier in the future. What we as fabric suppliers are saying is, that in order to keep the costs to the Australian community down, adopt one of the test methods that are already in use, (or plan to be implemented, overseas). The major fabric suppliers are already selling into all these major overseas markets and will already have these certificates, thus requiring no additional expensive testing in Australia. In our view there is nothing special about the Australian market that would require a different test here. Despite the perceived shortcomings of all these current tests the evidence is that they were successful in weeding out unsafe products for our industry as there is negligible to zero incidence of major fires or loss of life with materials that have passed these tests. Other Countries It is fair to say that other countries are also going through similar experiences. There are reports that in the US they are thinking about adopting new standards, and in parts of Europe they are similarly talking about adopting new standards. The European test method proposed is in fact very close to that proposed by Warrington, and that being the case we would suggest that this be adopted. At the very least if we are going to have a ’special Australian test’ make it a small scale test that does not impose undue financial barriers on the industry.
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A Regulator’s Dilemma: Case Study
John Shaw
H John is a senior advisor with the Technical and Research Services department of the Building Commission in Victoria. The Commission is the Victorian Government department responsible for the administration of the Victorian building legislation. H John holds a Bachelor of Technology (Building Surveying) including performance building codes and fire safety. H John has many years experience in the field of temporary structures in his role of coordinating the issuing of occupancy permits for temporary structures for use as “places of public entertainment”. H John is currently coordinating a research project into the fire safety of tension membrane materials used in the manufacture of marquees. A Case study is presented in which some dilemmas facing the regulator may impact on the industry.
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Flame Retardancy Disambiguation
Paul Knox Innova International i. Scope The presentation aims to explore issues regarding flame retardancy, its testing, regulations, and requirements placed on the lightweight structures industry with specific reference to tensile membrane fabrics. The presentation will look at the BCA 2007 regulations and clarify certain ambiguous entries that have led to industry confusion. Reference will also be made to the ongoing exploration of requirements for a new testing standard with specific relevance to the marquee and temporary structures market which has potential ramifications for all designers and manufacturers of lightweight structures. ii. Flame Retardancy – Imperatives Practical To ensure that the correct test is applied to all components, depending on the intended end use or location of the structure. To guide the industry in their interpretation of the BCA regulations to ensure certification does not hold up the development, tendering or construction process. [slide show of BCA2007 criteria that lead to confusion] To ensure that test reports are readily available to all relevant industry parties. Ethical To work with BCA authorities to guide the development of a standard that reflects the true requirements of the industry. Current testing measures four areas of interest: H Ignitability H Spread of Flame H Heat Evolved H Smoke Developed Only two of these criteria are actually then looked at by the BCA standards: H Spread of Flame H Smoke Developed [slide show of various requirements depending on end usage] These criteria are not particularly strict and, up until recently, have been quite easy to meet. As those present at the last LSAA Symposium would be aware from Brian O’Flaherty’s presentation, recent changes to the AS/NZ1530.3 testing methodology make this test extremely difficult for globally accepted architectural fabrics to pass. The important point to note is that this does not mean that these fabrics are deficient in terms of flame retardancy performance. Rather what it highlights very clearly is the unsuitability of the testing which was originally developed for materials quite different to ours.
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The status quo, if pre–2003 reports may be accepted, is sufficient, if barely. The BCA have implied, though not widely communicated, that this is acceptable to them. However from an ethical standpoint we should be pushing for a standard that measures the behaviour of these materials in a way that is meaningful to the end use. Measurements that should be taken include, but are not limited to: H Ignitability: With a desired ignitability level that opens the membrane to vent gases. H Behaviour: Does the material fuel the fire or self extinguish? Does the material rain flaming droplets? H Smoke: How much smoke is generated by the burning or smouldering material? Is that smoke noxious or harmful? [slide show of tent burn tests conducted by Ferrari] We must acknowledge that architectural textiles and they way that they are used can influence the safety of individuals within a fire situation, however the authorities must also understand that the membranes in and of themselves cannot make a fire situation safe. Not all variables can be managed within the confines of a test that focuses on membrane fabrics. Therefore, we as an industry must resist the suggestion of some individuals within the BCA revision process that the full focus of fire safety regulation be placed on membrane fabrics. Equal or indeed greater regulatory attention must be placed on the construction, placement and usage of structures. [examples from BCA meeting] iii. Conclusion A balance must be struck between practical and ethical concerns. Practically, we need a system that is as simple and financially accessible as possible for all parties: fabric suppliers, fabricators, architects, engineers and project managers. Ethically we need to accept that while we are aware of deficiencies in the current system and fail to act as an industry association we are all exposed to commercial and financial risk if we do not pursue a more appropriate testing outcome. In acknowledging this, the LSAA has a strong role to play in guiding discussion to prevent a future in which a prohibitively expensive or inappropriately harsh testing standard is designed and regulated due to insufficient interest or pressure from our industry.
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Fabric Life – Expectations and Experience
C.G. Tattersall Director, Tattersall Engineering Consultants Pty. Ltd.
INTRODUCTION Tensile structures incorporating architectural fabric have been built and used for many years, with the earliest air structure designs dating back to the early 1900’s. However it is really only since the early 1970’s that improvements in fabric technology and design procedures have brought tensile structures into common use in buildings. Unlike most other building products such as steel, concrete, timber, aluminium and glass, fabrics used in tensile structures have a limited history and the long–term performance of these early structures is only now able to be observed over periods compatible with other building materials, ie 30 – 50 years. This paper does not attempt to make an exhaustive review of the thousands of structures erected since the early 70’s, but focuses on a few structures with which the author has some experience or knowledge. The materials considered range from early Teflon–coated fiberglass (refer figure 1 –University of La Verne Sports Science and Athletic Pavilion – built in 1972) to PVC–coated polyesters with acrylic or pvdf coatings, to knitted high density polyethylene monofilament fibre fabric, commonly known as shadecloth, (refer figure 2 – shadecloth canopies at a resort in Northern Victoria). The actual performance of these fabrics is a factor in determining whether their use is considered successful or not. The expectations of the owners and the part they play in maintaining and operating their structures is another. EXPECTATIONS Fabric ’life’ is a very subjective term. It is expected that materials exposed to the elements will deteriorate, due to factors including:– H U V degradation H degradation due to other environmental factors (chlorine, pollutants, unsuitable cleaning agents, etc). H accidental physical damage, (bird strikes, falling objects, impact by construction or maintenance access equipment) H deliberate damage (vandalism or imprudent acts such as setting fires nearby).
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Figure 1 – University of La Verne Sports Science and Athletic Pavilion (California) Erected 1972, photo taken 2007
Figure 2 – Shadecloth canopies at resort in Northern Victoria Installed 1997, replaced 2006
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In looking at the expectations which owners may have about the life of fabrics, it is useful to examine typical warranties offered by the major manufacturers. This is a question often asked by clients considering the use of fabric structures; although warranties do not necessary provide an accurate indication of fabric life. FABRIC MANUFACTURER WARRANTIES Warranties typically offered on common fabrics can be as follow. Shadecloth(1) H 10 years against significant UV degradation of the shadecloth , typically restricted to replacement of fabric H sewing threads can be obtained with guarantees against defects and damage by exposure to sunlight, for up to 15 years, with the guarantee covering the cost of thread and customary expense of repair for any article sewn completely with the thread. H quality fabricators offer warranties on defects in workmanship for up to five years PVC–coated polyester, (including acrylic and PVDF surface treatments)(2,3,4) H usually 10 and up to 12 or 15 years, covering significant loss of strength, loss of water–tightness, reduction of fire resistance. H typical warranties cover replacement of fabric only; on a pro–rata reducing basis. Some cover a pro–rata reducing component of the total cost of removal, refabrication and re–installation of the membrane. This can be very important as the removal, refabrication and reinstallation costs can easily vary from twice to several times the cost of the fabric on the roll. The various manufacturers may offer different or extended warranties depending on the project and the client’s requirements. H generally an application has to be made for each specific project for the fabric used in that project to be covered by the fabric manufacturer’s warranty. Some manufacturers will automatically offer a warranty when an application is made for a structure, other manufacturers require the warranty to be applied for and approved prior to the fabric being ordered and fabrication commenced. H typical information required to be provided in a warranty application includes details of the project, the area to be covered, the proposed fabric, the location, diagrams and drawings of the project, who the engineer and fabricator are and any local environmental factors such as pollution levels, nearby industries, and exposure to traffic fumes. H claims under warranties must be made in writing within defined periods of time from when the defect becomes noticeable and must provide evidence of purchase and a copy of the warranty agreement including batch and roll numbers. H some manufacturers require a minimum 1m2 sample of the affected fabric (which may be problematic unless a sample piece of each batch is installed at each site under matching conditions for use on any future claim).
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H warranties often do not cover wear and tear, deterioration caused by exposure to harmful agents or conditions, incorrect or irregular cleaning, faulty installation, pretension or design, faulty manufacture, seaming problems, damage due to high wind loads or other unusual factors, mould growth due to inadequate air circulation and differences in levels of translucency between batches. H some extended warranties offered at additional cost cover 100% of the total costs of removing, refabricating and replacing the membrane for defined matters over the warranty period, whilst some cover solely the cost of the fabric. H it should also be noted that some issues experienced with surface coatings on fabrics are not strictly covered by the warranties and compensation for deterioration or losses becomes a matter of negotiation between owner, contractor and fabric supplier. Teflon Coated Fibreglass H warranties offered on Teflon–coated fibreglass typically extend over a 10 year period, and are limited to the original cost of fabric. Some are on a pro–rata reducing basis and some are not. Some cover only fabric replacement, others cover total cost of reinstatement but limited to the value of the fabric originally supplied. CONTRACTOR WARRANTIES Warranties offered by the contractor are generally determined by the building contract under which the project is constructed and a defects liability period of 12 months is common. Builders are also obliged under various legislation to provide further warranties in relation to structural performance or waterproofing for various periods as defined by legislation. This can vary from state to state and certainly will vary between countries. In practical terms most gross manufacturing defects (eg poor welding, improper coating of steelwork, cables not properly manufactured) are likely to become apparent within contractual or statutory warranty period, but where the defect arises from the original manufacture of the fabric it may take some years to become apparent. When this happens the builder or contractor generally has to rely on the warranty offered by the fabric manufacturer. This can become interesting because unless the faulty is explicitly covered by the terms of the warranty, assistance or compensation relies on the attitude of the fabric manufacturer. For example with fabrics suffering coating defects as some have, questions of ’fitness for purpose’ arise, and this goes back to not only to the wording of the warranty, the legislative requirements, and common law precedents, but also to the how well the owner’s expectations and requirements have been defined as part of the original contract. This can easily become a very grey area.
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DESIGN ISSUES Fabric structure performance and life should not be compromised by design issues but unfortunately some structures have been known to suffer premature failure due to a lack of rigorous engineering design. This is more common with smaller structures and shadecloth structures, but can happen with larger structures if design issues are overlooked. Common design problems can include H poor surface shape or a lack of pretension allowing ponding and failure due to rainwater collection H failure of supports due to inadequate assessment of loads developed by the fabric membrane H damage to fabric caused by excessive deflection, vibration or fluttering, usually as a result of inadequate pretension H poor detailing leading to overstressing of fabric (often in a tearing mode) either in–service or during installation or handling Whilst no procedures can provide an absolute guarantee that design issues will not arise, prudent clients and project managers will ensure their structures are designed and certified by engineers with detailed knowledge, specialist experience, and a comprehensive track record with design of tensile structures (LSAA consulting engineer members are generally a good place to start when seeking a suitable engineer). Even within the quite narrow field of tensile structures there are areas of particular expertise, as design and detailing for coated fabrics such as PVC–coated polyester and Teflon coated fiberglass require quite different approaches to knitted shadecloth. Because a designer may be expert in large coated fabric structures this does not necessarily mean they will be experienced with shadecloth structures, where the design imperatives of scale and economy can be much more stringent. Any competent engineer experienced with tensile structures should be able to design a shadecloth structure which is structurally adequate, but designing a structure which is not only structurally adequate but economically competitive in the marketplace can be another issue. OWNER EXPECTATIONS AND MAINTENANCE The essential factor in a tensile structure being considered successful is the expectations and input of the owner or operator. Whilst tensile structures can be remarkably resilient to abuse or neglect, they will certainly provide better performance and give better service life if they are properly cared for by the owners. The ’life’ of a fabric can be a very subjective matter. If a fabric membrane is installed in an application where the top surface is not visible from any close location, and variability of transmitted light is not a major concern, then a build up of soiling and dirt or a loss of gloss may not be an issue. Indeed anecdotal evidence suggests a persistent coating of dust on the Yulara ’sails in the desert’ structures allowed the membranes to survive in extreme UV conditions from when they were installed in 1984 until their replacement in the last few years. However, if a high gloss retention and top surface shine is important to the owner, structures benefit from being cleaned regularly. Some warranties require structures to be cleaned at not more than 12 month intervals, and some projects constructed by the author have maintained a reasonable level of surface gloss over more than 10 years with regular cleaning on a 6 to 12 month interval. Periodic inspection is essential and regular cleaning can contribute to an improved fabric life, although recent advice from some manufacturers is that excessive cleaning can in some circumstances lead to deterioration in fabric life.
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Different fabrics also respond differently to soiling and cleaning. Some fabrics can display distinct lines of soiling, and it is not clear whether this is due to the fabric itself, or due to factors associated with manufacture and handling. The author does note, however that fabrics from some manufacturers do tend to display this effect when fabrics from other manufacturers, which to the author’s knowledge are manufactured and handled in exactly the same manner, do not. EXAMPLES AND CASE STUDIES Shadecloth Case Study S1, shadecloth structure utilising 5 membranes totaling about 1200 square metres in area, over a resort swimming pool in Northern Victoria. (refer figure 2 earlier in this paper). This was first erected in 1997, as a replacement for membranes of different materials, construction and design, which had suffered structural failure a short time after installation. An elegant design, utilising a number of layered profiles overlaying each other and generally inclined to the north, the structure allows sunlight penetration to the pool areas during winter and cooler months whilst providing several layers of shadecloth for increased shade density in summer. By late 2006 the membranes were suffering deterioration due to a combination of stitching deterioration under UV, physical damage due to vandalism and bird strikes, and seams being highly stressed by unauthorised access by a number of people climbing on the panels at one time. They were replaced with new membranes utilising improved stitching with a guaranteed 15 year UV resistance and hopefully will provide many years of reliable service. Case Study S2, a shadecloth conic at a primary school in the northern suburbs of Melbourne, erected in 2000. This suffered some deterioration of the shadecloth around webbings, possibly due to UV deterioration, but also possibly due to birds pecking at the fabric, seeking insects or spiders at the peak (refer figure 3). The structure was taken down in 2006 and the damage repaired, and is still in service.
Figure 3 – Shadecloth structure at School, installed 2000, repaired 2006
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PVC–coated Polyester Case Study P1, an iconic project in the northern suburbs of Adelaide, the first stage constructed using a pvc–coated polyester with acrylic lacquer in 1996, and a second stage using a different manufacturer’s fabric in 2001. These structures were regularly cleaned, generally at least once and usually twice per year. Soon after installation some coating problems were experienced with the second stage and the membranes were replaced. The first stage fabrics are still in place although one panel suffered mechanical damage from a boom lift being used during cleaning in 2006. A significant tear occurred, and the membrane was taken down and a section of a panel replaced. This provided an opportunity to have the fabric tested to see how it had performed over 10 years. Comparison of the original specified properties and the measured properties is presented in table 1 (courtesy of Mehler(2)).
Property SAMPLE Specification Total weight gsm 760 ~800 Tensile N/5cm 2949/2388 ~3000/3000 Tear N 280/200 ~ 300/300
Table 1 – tested properties of PVC–coated Polyester after 10 years of exposure in Adelaide This indicates a slight but quite reasonable deterioration in physical properties. The decrease in tensile strength is low and the tear strength acceptable considering the years of exposure. Flexibility was considered as ’medium/hard’ which is expected after 10 years. What is more obvious however, is the visual appearance, and there was a quite distinct difference in gloss, colour and translucency between the original fabric and the replacement fabric, which was of a similar grade although with a weldable pvdf coating instead of an acrylic coating (refer figure 4)
Figure 4 – repair of tear in PVC–coated Polyester membrane, installed 1996, repaired 2006
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Case Study P2. This was a small twin conic erected in 1990 and was to the author’s knowledge the first application of a PVDF/PVC coated polyester fabric in Australia. The structure was designed by the author and the fabric selected as a trial since the small scale minimized economic consequences if the fabric performed poorly. It has now been in place for nearly 17 years and is still performing well, having been cleaned and relocated on a few occasions (refer figure 5).
Figure 5 – twin conic in pvc–coated polyester with PVDF, erected 1990, photo October 2007 Case Study P3. PVC–coated polyester structure with PVDF surface, erected in 2000, suffered a severe failure of the PDVF laminate in late 2003, not affecting structural integrity, fire resistance or water–tightness, but causing a reduction in gloss of the surface and an unsightly appearance as dust and soil builds up under the delaminating coating. This requires regular cleaning to remove the delaminated coating, when hopefully a uniform appearance will be restored. (refer figure 6)
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Figure 6 – delamination of surface coating on pvdf/pvc–coated polyester, installed 2000, coating issue arose at end of 2003 Case Study P4, A barrel vault canopy of erected in December 2001, showing considerable soiling in defined lines, but not at valleys, prior to the first clean in June 2004 (refer figure 7). The fabric was installed taut at pretension levels of 1.5x1.5 kN/m and has no wrinkles or defects, but soiling was apparent at lines which may have been where the fabric was folded during manufacture, transport and installation.. The soiling cleaned off and a uniform glossy surface was restored with normal cleaning following recommended procedures.
Figure 7 – soiling in lines on surface of weldable PVDF/PVC–coated polyester
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Teflon Coated fibreglass Case Study T1, The Sports Science and Athletic pavilion at University of La Verne, California. Erected in 1972, this was one of the first Teflon–coated fiberglass fabric structures ever built. The author reported on this structure in 1985(5) (refer figure 8), when it was still performing well. Recent advice from the owner(6) is that it is still performing well, 35 years later, and the fabric has not lost a significant amount of its original gloss. The interior liner did not last as well as the exterior fabric and has been recently replaced.
Figure 8 – University of La Verne Sports Science and Athletic Pavilion (California) Erected 1972, photo taken 1985 Case Study T2. A private residence in the Yarra Valley had an atrium of 400 m2 covered with square based conic using Teflon–coated fiberglass, built in 1982. Advice is that it is still performing well, 25 years later. It is regularly inspected and cleaned each few years CONCLUSIONS Fabric life is very dependent on the acceptance of the owner of the appearance of the fabric. Many fabrics will still perform in terms of structural capacity and watertightness, many years after their surface may have lost a substantial amount of gloss and may be appearing quite dull. The life of an individual project cannot be predicted with certainty since it is dependent on so many variables, but some examples indicate that:– Shadecloth can reasonably be expected to last 7–10 years but owners should consider budgeting for replacement after that time. Stitching is a critical item and due consideration should be given to use of UV resistant stitching and protection of stitching by the means of construction (especially when webbings are used) PVC–coated polyesters seem to have a reasonable service life of at least 10–15 years, and some may last for many more years. Cleaning and environmental factors can have a significant effect.
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Teflon–coated fibreglass seems to last at least 20–25 years and may last much longer. Capital costs may mean that life–cycles costs may be cheaper if one uses PVC–Coated polyester and replaces it periodically, but this is dependent on a many factors including ease of replacement, disruption during the process, and original project costs. Generally fabric structures will provide good value as long as owners approach projects with realistic expectations. Less expensive products tend to have a shorter life but be easier and less expensive to replace. What is essential with any fabric structure is for the owners to have realistic expectations about the performance of the solution they choose, have it properly designed, and follow recommended maintenance procedures. In this manner we trust that fabric structures will continue to provide good service, excellent value, and eye–catching architecture in more and more projects over the coming years. Acknowledgments and references 1. Gale Pacific and Oasis Tension Structures, for information on shadecloth fabric 2. Indtex, for information on Mehler fabrics, and fabric testing 3. Halifax Vogel Group, for information on Verseidag fabrics 4. Innova International, for information on Ferrari Fabrics 5. Tattersall, C.G, Fabric Membrane Structures and Community Buildings, I E Aust National Engineering Conference, 1985 6. Mr. Robert Beebe, Assistant Director of Facilities Management, University of La Verne
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Robina Stadium
by Mr W.Chalmers HOK Sport Architecture
Introduction On 27th of May, 2005 the National Rugby League (NRL) announced that the 16th NRL franchise had been awarded to the Gold Coast consortium, known as the Gold Coast Titans, with this new team entering the NRL Premiership competition as of the 2007 season. Central to the successful bid and emergence of this new team was a new 25,000 seat rectangular field stadium to be constructed in the Gold Coast region that would host ’home’ matches as of the 2008 season. In June, 2005 the Gold Coast City Council commissioned HOK Sport Architecture to review several shortlisted sites in the Gold Coast area that they believed could adequately house such a stadium. From this feasibility process a 4.8 hectare site at Robina was selected. The chosen site(Figure 1) is to the north of the Robina Town Centre and within 500m of the Robina Train Station which is the current southern terminus on the Brisbane–Gold Coast rail line and approximately 8km direct from the coastline. Although the identified site and its adjacent plots of land are free of any built environment it was envisaged that the stadium would act as catalyst for future commercial, retail and entertainment development in the adjacent site areas.
Figure 1. Aerial shot showing the stadium location at Robina and within the city of the Gold Coast. Design Competition In September, 2005, the Queensland Government through Project Services held an invited design competition for a 25,000 seat regional stadium to host the new Titans franchise and to be located at the above site.
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The key brief requirements of the Design Competition were as follows; H Limited budget. A construction of budget of $120 million was set. H Capacity of 25,000 seats minimum. H Tight Timeframe. It was imperative that the new stadium be open in time for the start of the 2008 season, i.e. March 2008. H Roof Coverage to at least the West Stand. H Integration of stadium within immediate environment. HOK Sport Architecture won the design competition through the following design concepts that fulfilled and exceeded the above design parameters. Creation of Atmosphere The stadium is designed to achieve maximum spectator atmosphere and experience. This is achieved by two key building components, namely the roof and seating bowl, working in tandem. The seating bowl is a single wrap around tier to achieve the closest seating configuration as well as the maximum coliseum effect. To promote such an effect it was seen as critical that there was a level of equality with regards to size for each of the four stands and not load the side stands substantially more than the end stands.
Figure 2. Some of the early seating bowl design options. The image on the right shows the option chosen. Given the tight design construction budget we had to achieve great efficiencies in the seating bowl design to allow expenditure to be directed to the incorporation of a substantial four sided roof within the cost plan. We achieved these efficiencies through three design directions for the seating bowl; H Concentration of highly serviced corporate and membership areas into the Western side of the stadium. H 3 sides of the stadium accommodate general admission seating in a simple repetitive structural and circulation solution. H The stadium section is an ’at grade’ solution on 3 sides. A roof was designed for all 4 sides of the stadium to achieve the maximum sense of enclosure as well as providing retention of sound and light and protection from weather. One of HOK’s core beliefs was that the provision of a roof on all sides is critical to the successful atmosphere and acceptance of the stadium. There have been a number of regional stadium developments in Australia over the last few years that have shown the poor results of developing a single sided roofed grandstand or independent sided grandstands.
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The roof was designed in a simple repetitive cantilever structure, that could be erected in component stages. The roof structure also provides the external walling enclosure to 3 sides of the stadium. The drip–line coverage of the roof provided is just under 80% of all seats. The precise position of the leading edge of the roof was dependant on the costing parameters for the roof and the design allowed for flexibility for this position. What was critical was the provision of the roof on all 4 sides of the stadium, not necessarily the amount of drip–line coverage. Identity Gold Coast’s position as the premier holiday and entertainment and Australia’s fastest growing city make it a unique destination and one that is constantly developing. The development of the city is dominated by the high rise skyline of Broadbeach and Surfers Paradise with its absolute beach frontage looking over the Pacific Ocean. The sun, surf and sand combined with the clean fresh air of the Pacific and the relaxed outdoor lifestyle define the Gold Coast. The Gold Coast can boast an average of 245 days of fine weather each year and daytime temperatures above 22 degrees for 279 days a year. The notion of developing an architectural character for the region to reflect this lifestyle is one that is still evolving. A defined language for residential towers has long been established. The architectural character of Broadbeach and Surfers Paradise with their concrete and glass facades punctuated and animated with balconies to make the most of the views and outdoor lifestyle has defined high rise residential developments for the last two decades. But what character defines the hinterland and the heart of the city away from the bustling seafront strip? This has generally been an eclectic mix of architecture that has failed to define a city centre or create a sense of urban density. The Robina Stadium and the associated development opportunities provide the chance to create a urban centre for the Gold Coast away from the beach, a place that can be use by all aspects of the community 365 days a year. The issue in developing an architectural response that reflects the character of the Gold Coast was core to our design approach. The notion of developing a light open stadium covered by awnings and shade structures creates a compact yet enclosed form befitting of the outdoor lifestyle of the Gold Coast. The stadium has been designed with a purity of form and attention to detail that will give the building a grace and power befitting of the emerging Gold Coast sophistication. This building is not only about portraying obvious structural gymnastics, but instead presents a form that is relevant to this location. The building identity aims to achieve the following presentation; H A building that expresses the dynamic movement of sport H A building that expresses a festival atmosphere H A building that responds to the gold Coast climate and outdoor living H A building that captures the strong quality of sunlight. H A building that expresses it’s different functional parts. There are however references to the more iconic Gold Coast images of surf, sun and the beach. We must not forget that this building must present itself to the Australian television audience and show its identity as unique to the Gold Coast image.
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Roof Architecture
The design of the roof is key to the success of the stadium’s design in that it is the centrepiece of fulfilling these two core design concepts of creating atmosphere and identity.
The realisation of creating such an identity is achieved primarily through the roof architecture of curved roof rafters and a PTFE fabric roof covering. The curved section shape of the roof is an effort to contrast with the horizontal forms of the surrounding buildings and also provides a wonderful sense of space in the seating areas and provides a metaphor of the movement of ocean waves and sports endeavours.
The fabric on the roof has been used in a very planar way and we have avoided the obvious tented structures to reinforce the purity of form. The roof will be lit at night to enhance the glow effect that will come from the sports lighting and make this a beacon in the evening.
Figure 3. Presentation image showing the stadium at night.
But apart from all these symbolic meanings and architectural nice–ities the roof has a significant amount of practical gravitas to it. From a build–ability, operational, spectator comfort and cost viewpoint the roof architecture has significant benefits.
Construction wise the roof rafters are composed of three box rafter sections that allow for fabrication off site which provides for a higher level of quality assurance and accuracy. This method reflects the preferred approach of the construction of the stadium as a whole – i.e. where possible off–site fabrication and then installed sequentially on–site. Furthermore, the design of the roof frame aligns and interfaces with steel frame of the seating bowl that allows for a simple, elegant and importantly time and cost effective design solution.
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Figure 4. Images showing the sequential construction of the North stand.
At an operational level the roof profile is of sufficient height such the underslung catwalk can house the sports lighting for the field of play that then negates the need for light towers and their associated cost and light spill and glare impacts. Further to this the PA and other audio related services can be installed on such a platform. The PTFE fabric also has an operational benefit through its self–cleaning and low maintenance qualities.
The intensity of the sun also means that the provision of a roof over as many spectators as possible is a very desirable feature. The provision of shade is most important for spectators and is a balance with the amount of shade on the pitch for grass growth.
Furthermore, the wind conditions of the Gold Coast allow air movement and ventilation to alleviate the ever–present humidity of the South–East Queensland region. As such the upper levels of the façade on the South and East sides of the stadium encourage air flow by the provision of slots in the lap of the roof fabric that along with the vomitories opening provide for air movement and hence cooling to occur across the spectator stands as well as the pitch.
Where the stadium touches the plaza, shade overhangs, referred to in the project as the ’skirt roofs’ are provided by the skirt roof to give both a human scale as well protection from the elements.
Urban Design Response – The Integrated Stadium
This is not a stadium in a ’greenfield’ site in the true definition. The design is responding to its urban village location in what will be a built up surrounds of 8 stories massed commercial /retail buildings. As such, the stadium and external concourse are designed with this in mind – that is the stadium is an intrinsic part an overall entertainment and commercial and even residential precinct – that is, it is an integrated stadium.
Visually, the stadium is in scale compatible with the intended scale of its neighbouring development but provides a counterpoint to the architecture and massing of the surrounding building by its lightweight and curved forms. The bold statements of the stadium forms will read legibly from a distance as well as from close distance.
The western face of the stadium is exposed to the train line and surrounding areas and as such a feature is made of the contrast of the blue metal sheeting enclosure of western accommodation with the PTFE roof forms that form the majority of the stadium. The building will make a bold statement from the long distance western view. The building reveals itself in a more subtle way on the eastern side as one approaches the building at close range, never being presented with a long range view.
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This eastern side will be the major pedestrian accessway on event day and the sense of discovery and understanding that people are on a journey to the stadium through a built up urban block is important in informing the design. The increasing sophistication and urbanisation of the Gold Coast we felt deserved and architectural response to site that is intelligent and exciting.
The roof architecture on the eastern and to a lesser extent southern sides responds accordingly to this design approach. The roof fabric of the main stadium roof steps back within the roof rafters breaking down the scale of this façade. Augmented to this is a change of fabric material to a more translucent mesh material that allows a certain level of transparency to the building on this side, especially at night time. Further the skirt roofs, as noted above, provides amore human scale at these two sides. The stadium was placed as far as practically possible to the North–West part of the site so as to create a major urban space to the south–east. The south east corner is the most important for arrival of the majority of spectators and as such the presentation of the building responds to that. The stopping of the skirt roof in the corners and the upward curve of the PTFE fabric slot are done to give emphasis to this corner and signify the major entry point of the building.
Figure 5. Presentation image on left showing stadium from South–East corner and construction photo taken in late September 2007.
But on a pedestrian activity and flow aspect the creation and size of this South–East plaza is integral to the success of the stadium on game day but also to the amenity and pedestrian enjoyment of the precinct on non–event days. Our design response was to create a public plaza in this corner that was similar in nature, albeit smaller, to the Caxton Street End Plaza that exists at Suncorp Stadium in Brisbane by acting as an attractive catchment area for entering spectators, that allows for people to meet and dwell in an attractive external environment before entering the stadium.
This is achieved through the creative implementation of paving treatments, hard landscape elements such as precast concrete benches and soft landscaping elements that not only break down the scale of the open space.
Furthermore, it was felt that such a design approach responding to a just as important obligation to provide an appealing breakout space for the local population during the week, whether they be office workers or residents of the precinct.
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Building Sections Many section studies were undertaken to determine a suitable design solution as shown in Figure 6.
Figure 6. Initial concept sketches for the seating bowl/roof section. The overall stadium section has been designed to avoid any below grade basements or pitch. This is partly due to flooding levels on the site, as well a method for achieving simple design and efficient construction. The stadium has two general sections – one template for the north, east & south stands and another for the west stand. The north south & eastern sections are all a simple single tier with either toilets or food and beverage concessions located underneath. As noted before the raker beams that support the precast concrete plats that connect to the roof rafters hence making an integrated roof/seating tier frame system. We have also designed the north , south & east section to be the same depth to reinforce the coliseum effect , as well as providing cost effective construction. With a capacity of 25,000 seats it is necessary to reinforce the coliseum effect to achieve maximum atmosphere, that can be so lacking on stadiums of this capacity. This was also fundamental to the decision to wrap the seating around the corners, so that atmosphere does not leak out of the stadium. There are ’bites’ taken out of the seating tier on all four sides. This allows for placement of scoreboards in the north–east and south–west corners. Additionally such void spaces create impressive atrium spaces in all the corners, notably in the south–east corner which is the ’front door’ of the stadium and the North–West corner where a bar with associated milling space is being incorporated. On the western side a separate suite tier has been designed to allow the close proximity of the suites to the field as well as a premium experience. (i.e. not at the back of a tier). The separate suite tier also allows the Level 2 function rooms underneath to have views of the pitch. The overall section for the West stand differs quite substantially from the general section that is used for the North, South and East stands. This is due to the amount of extra accommodation found on the side such as all the BOH spaces, Function rooms and plant areas. This necessitates that the building form ’punches’ out of the standard section enclosure. As it was a conscious decision to make this element a point of difference to the rest of the stadium whilst not dramatically changing the architectural language. As a result the West stand is mainly comprised of a ’pod’ element that is clad in metal sheeting as opposed to fabric and is blue in colour as demonstrated in Figure 7 below.
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Figure 7. Presentation image showing west stand accommodation and September construction shot. Spectator viewing values, noted as C–Values, are minimum C90 which in comparable terms means that a high standard of viewing is provided. The section has been carefully calculated to achieve the best standards of disabled provisions. Wheelchair and ambulant disabled positions have been distributed through all levels of the tiers. As noted previously the leading edge of the roof has been design at a suitable height for sports lighting at a minimum 25m above the pitch to avoid the need for light towers, so that light spill is minimised. The sports lighting engineers designed the lights to work well at this height without the need for towers. Also this allows the building architecture to be defined by the building form rather than appendages. The section also shows that the roof structure continues to ground level and provides the frame for the external wall envelope of the building. This allows an efficient cantilever and good coverage to the concourses from the sun but also wind driven rain. Ground Floor Plan Core to the success of any stadium is the ease of crowd circulation. Circulation within the stadium is planned with maximum clarity and simplicity. The stadium has at grade circulation for the general admission seating. The entry and concourse are easily accessed from the plaza areas . The building perimeter is permeable and allows for a visual connectivity between the concourse and the external plaza and the street. The general admission spectators access via a main bank of turnstiles on the south and east sides of the building. The concourse as shown in Figure 8 is a light, airy and naturally ventilated space that is sized to handle significant internal circulation flow of people and is serviced by the appropriate amounts of toilets and food and beverage concession units. Access to the seating bowl is by vomitory ramps that used to allow access for people in wheelchairs.
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Figure 8. Presentation image showing Eastern concourse accommodation and September construction shot. The majority of the back of house facilities are on the western side of the stadium , to give efficiency of planning and direct service lift access to the serviced levels above. The service road in this location is full 4.5M clear height to allow the players’ coaches direct access to the facilities and pitch. Corporate spectators located in the west stand enter the building in the south west corner of the building though dedicated turnstiles then move up to the members concourse on the western stand. Suite patrons enter the stadium from the western corporate entry drop off using the lifts direct to level 3. The western side of this level contains all the required back of house facilities, including players facilities, press facilities, Main Production Kitchen & store facilities, staff facilities and venue management. Level 1 This level, specifically the concourse, has been designed to a slightly higher level of finish to accommodate the stadium members and corporate spectators who sit in the tier on the premium western side of the ground. Like the Level 0 concourse concession & toilets are located throughout the concourse and the crowd density of the concourse is significantly lower than the Level 0 concourse. Level 2 This level locates the function room with views over the pitch with direct access to finishing kitchens. The finishing kitchen is located on this level as well as the radio commentator booths and the Coaches Boxes. Level 3 This level locates the suites. The suite level is separated from the lower tier to provide a premium facility, have the best possible view of the field, as well as the ability to expand the viewing member facilities or function rooms below. The suite numbers and sizes are provided as per the brief. The suites are located in the closest proximity to the pitch of any major stadium in Australia to provide the best possible corporate facilities. The finishing kitchen is located with direct service lift access from the stores and main kitchen. The media suites are also provided in the key location to allow the best possible media coverage.
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Conclusion The primary design aim of the stadium was to provide maximum atmosphere as well as providing a unique and relevant backdrop for the screening and promotion of the Gold Coast to a national sporting audience – in the most cost–effective manner. Given there would not be the mass of 40,000 plus spectators to produce atmosphere the core objective was to produce a seating bowl and associated building envelope that would optimize and retain the atmosphere of any size crowd. As such the seating bowl is a tight wrap–around single tier with a small cantilevering suite level on the west side. All four sides are generally equal in size and the corners are cut–out. Encapsulating this tight seating bowl is a steel framed skeleton of curved steel box rafters (over 2m thick at their widest) that transform from being the wall section to the roof section. The design approach has been to clad this frame in a material that was reflective of the Gold Coast ’feel’ and climate of strong light, breeze and a general air of informality and recreation. PTFE roof fabric was chosen as it was believed the material best represented these qualities due to its lightness, transparency and fluid form. When these three elements of intimate seating bowl, tight frame and PTFE cladding are combine what results is an atmospheric stadium of imposing form and original character that is truly reflective of the Gold Coast.
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Stretching the Boundaries of Membrane and Film: Robina Skilled Stadium and Clarke Quay
Peter Lim Tensys
In many ways the fabric structures industry has matured. The use of structural membranes is now more commonly seen as just another building option rather than something exotic and different. There is now a very wide range of projects in locations across the world. The form and detailing of tensile structures is deceptively clear and simple. However these are still complex systems that require care in design, detailing, fabrication and installation. The continuing development of fabric clad stadia roofs has provided structures where not only the cladding but also the supporting system has been optimised for both efficiency and aesthetics. The new Robina Skilled Stadium in Australia features not only a tension fabric roof structure but it is further enhanced by a translucent tensile membrane façade wall structure. Some buildings continue to push the envelope of form and function. Conceived by SMC Alsop are the sculptural shade elements for the streetscape of the renovated Clarke Quay riverside area in Singapore. These use a mixture of PTFE coated glass and ETFE. The growth of use and architectural interest in ETFE foil as a cladding material is probably one of the strongest phenomena in Europe at present, and this effect is spreading towards Asia. New applications and materials continue to challenge the designers and builders of stressed membrane structures. This presentation is intended to stimulate further possibilities. Robina Skilled Stadium and Clarke Quay are presented in a little more detail on the following pages. Project Robina Skilled Stadium, Gold Coast Australia Description Robina Skilled Stadium (under construction) is to be the new 25,000 seat rectangular (in plan) home of the ARL team Gold Coast Titans. The stadium terraces are covered with a roof constructed from curved steel box section rafters interlinked with CHS purlins and clad with PTFE glass tensioned fabric panels. The playing surface is open to the elements. Steelwork The roof steelwork is formed from fabricated steel plate box section ribs or rafters. The rafters are spaced at 10m centres forming a regular grid along each of the four sides of the stadium. The rafters truncate and mitre into diagonal rafters at each corner. The curved rafters span from pinned connections at entry terrace level curving out and away from the grandstands and then up and over the seating area. The rafters are tied into the terrace structures approximately 14m above entry terrace level and then cantilever 28m beyond this point. The rafters are 350mm wide and vary in depth from 620mm at the base pin to 2340mm at the prop and back down to 360mm at the tip. This is the situation along the North, South and East wings.
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Along the West Wing is the main entry structure that projects out through what would be the lower roof area and so upper roof rafters’ cantilever from the top of the entrance structure.
Fabric The rafters form the boundaries dividing up fabric panels that are attached and tensioned to the faces of the rafters. Each bay between the rafters is divided into two regions; an upper ”roof” panel and a lower ”wall” panel. The edges of these regions are defined by purlins spanning between the rafters. The fabric is also attached and tensioned to these edge defining purlins. There are also some internal purlins spanning between rafters to help brace the rafters. The fabric is intended to sit clear of the internal purlins under all conditions. The upper roof panel of fabric is fabricated from conventional PTFE coated glass weave fabric. Along the South and East Wings lower wall panels the architects have proposed that the conventional fabric makes way for a fabric of much higher translucency. This panel is offset inwards towards the stadium from the line of the roof panels; the architects intent is as if the conventional roof panel has been torn away to expose the interior workings of the grandstand behind. A PTFE laminated glass weave mesh fabric with approximately 50% light transmission compared with 10% for the conventional material was adopted. Wall Panels in the North and West and at all corners are fabricated from the conventional fabric. Roof panels are subject to high uplift forces. The roof panels are reinforced with a valley cable system that acts to stiffen the panels and reduce fabric stresses under the uplift load cases. It is intended that the valley cables are only notionally prestressed at installation and so they have little effect at resisting downwards wind pressures. The fabric works on its own under these conditions. Wall panels on the other hand are subject to high inwards pressure wind loads. In particular, the South West corner panels are heavily loaded. The original intention was for the wall panels to also have valley cables, however these had no practical function in resisting the high inward pressure loads and were deleted.
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Installation Hightex have brought their novel approach to installation that is a variation on their proven methodology used to install fabric panels at Bangkok Airport and Berlin Stadium. The use of expensive conventional access equipment and fixed scaffolds are minimised. This methodology was approved by the local workplace health and safety authorities following a stringent review of the procedures.
At time of publication, many of the conventional fabric roof and wall panels have been installed and the first laminated mesh wall panels have gone smoothly into position.
Contributors Client Major Sports Facility Authority Queensland Government Architect HOK Sports Architecture Engineer SKM Main Contractor Watpac Limited Specialist Contractor Hightex Membrane Engineering Tensys
Project Clarke Quay, Singapore
Description The current redevelopment of the riverfront at Clarke Quay brings new shopping and dining facilities whilst trying to maintain some of the ambience of the old fishing village that had become a hub of trade and industry.
SMC Alsop was engaged by Capitaland to create a new Singaporean landmark with the redevelopment of Clarke Quay in Singapore. Local Singaporean architectural firm RSP Architects worked as the local documentation and project architect.
Clarke Quay is a riverfront neighbourhood composed of 100 year old Chinese dockside shop fronts and rice godowns. This area was redeveloped in the late 1970s, but over the years it is looking tired prompting Capitaland to redevelop it as a major tourist precinct with cafes, restaurants and nightclubs.
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There are two distinct areas to the development. Alongside the Singapore River the promenade has been extended by ”Lily Pads” that are 0.5m above ground level and and extend by up to 1.5m out over the river. Continuing the botanical theme, the waterfront is covered by a series of over 100 ”Bluebells”, 4m and 5m diameter PTFE glass canopies with a form resembling the flower.
The second area comprises of canopies providing shelter for the 4 main internal streets and the central courtyard of Clarke Quay. Approximately 7500m2 of double layer ETFE and 3800 m2 of single layer ETFE are supported by steel ’angels’ towering over the adjacent buildings at 16m above ground level.Along the Riverfront is a strip of outdoor dining areas with Riverfront Canopies.
Stylish street furniture has been created by the architect to provide not only shade and shelter, but also strong visual interest by day and night.
Bluebells The Bluebells are dome shape structures that are fabricated with an exterior steel skeleton frame (a series of hoops and ribs). The frames are clad with tensioned PTFE glass fabric that is tensioned and attached to the interior of the frame. There are two different modules; a 4m and a 5m diameter dome that are seemingly suspended from curved steel masts.
The structures are challengingly intricate for PTFE structures with great accuracy required in detailing, patterning and fabrication.
The irregular interstices between the Bluebells are filled with a tensioned PTFE glass fabric panel ribbons that flow over arches linking the Bluebell frames. The ribbons also flow around trees growing up between Bluebells.
Providing weatherproof coverage from the Shopfront facades to the Riverfront Canopies are a series of Link structures.
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The Links structures are shallow PTFE cone structures with catenary cable edges with external steel frames attached to slab level at the facades (slab levels vary from one building to the next). The structures cantilever over the quayside street and overhang the Riverfront Canopies. The Link structures can be raised by a retractable arm with the canopy pivoting at the building face to allow clearance for transit of emergency vehicles.
Angels These structures are the first use of ETFE in Singapore and so there was much work required to satisfy regulatory authorities for it use on this project. Hightex and Tensys worked closely with the architects to get the concepts approved. Tensys also worked closely with the architect to develop a suitable rational geometry and structural system to support the canopy. The structural system is a series of spiral truss columns that zigzag from side to side along each of the four legs along streets leading to the central crossroad area. The zigzag helps to provide some stability and also decreases the uniformity that the architect was trying to avoid. At the head of each truss column is a series of twelve radial arms that crank in elevation and overhang the shopfront buildings along the sides of the streets. The arms are stayed with tension rods both above and below. At the central cross road area there are four tall spiral truss columns interlinked with rod stayed radial arms that also crank and cantilever over the street canopies and corner shop front buildings. Each of the four street canopies and central canopy are structurally independent of each other. Each spiral truss column is capped with a large polygonal ETFE cushion and each of the radial arm frames are clad with ETFE cushion structures. The ETFE has an intricate organic frit pattern printed on its surface to provide some shading. At the ends of each radial arm, the arm cranks down to provide some weather protection as the structures cantilever over underlying shop fronts. The cranked regions are clad with tensioned single layer ETFE skins.
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Rain on the ETFE cushion structures drain into box gutters at the head of each truss and thence into downpipes that are hidden inside structural members. A siphonic drainage system was adopted to minimise downpipe size. Contributors Client Capitaland Commercial Limited Architect SMC Alsop Engineer Tensys Main Contractor Kajima Specialist Contractor Hightex (Angels) & Rightech (Bluebells) Membrane Engineering Tensys
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Project X experiences of multidisciplinary Arch/COFA/Eng teaching
Z.Vrcelja, M.M. Attarda, G. Bellb and C. Longbottomc aFaculty of Engineering, UNSW bFaculty of Built Environment, UNSW cCollege of Fine Arts, UNSW ABSTRACT The present paper describes two multidisciplinary design courses, named Project X and Project X2, that were available for the first time in 2007 to students from three design–based faculties at the University of New South Wales (UNSW): Faculty of the Built Environment (FBE), College of Fine Arts (COFA) and Faculty of Engineering (FE). During these courses, the students designed, fabricated and constructed from cardboard and timber an enormous sculpture of a snake, nick–named Ed and consisting of five massive arches and a five meter tall head. Ed was displayed for a period of five weeks on the UNSW main walkway to celebrate multi–disciplinary design education and the ConnectED2007 Conference. In addition to discussing Project X, this paper also explores some of the challenges in education of today’s structural engineers and the benefits of the newly introduced BE Civil Engineering with Architecture Program at UNSW. PROJECT X The project consisted of two parts, namely Project X and Project X2. Project X, the scheme design course, was run as an intensive three–week course in February 2007. Students from the three Faculties worked together in teams to produce scheme designs against a brief set by the ConnectED 2007 Conference Organising Committee, the actual Client. (The ConnectED Conference, held at UNSW in July 2007, provided a platform for the discussion of research and strategies that address the promise and possibilities of design education that crosses disciplinary boundaries.) The scheme designs were evaluated first within the course by the Interim Jury and then by an external Project X Final Jury. The Final Jury selected the winning design which was then further developed, fabricated and constructed by multidisciplinary teams in Project X2 (the Fabrication and Construction Course). The brief invited a design that was a building, or a sculpture, or some other sort of intervention or installation that would symbolize the theme of the Conference. The design brief included artistic, formal, functional, loading, sustainability, budgetary, and other performance criteria. The design concept (the final product) had to be capable of subsequent fabrication and construction. The site for the erection of the selected project was chosen to be at the heart of the campus, the main walkway just below the Scientia Building, the venue for the Conference. This framework provided staff and students from the three Faculties with an opportunity to work together by applying their skills on a real project, with real time constraints and a defined budget. Project X was held at COFA in a large studio space sufficient to accommodate 65 students, 4 full time members of staff and various guests. A workshop studio environment was adopted with teams of three to four students working on the ”open ended” design brief, with approximately equal numbers of representative students from the three Faculties. Students came from a wide range of design–based undergraduate degree programs: Civil Engineering, Architecture, Design, Industrial Design, Fine Arts, and Building Management. Coursework included lectures, individual research, design, team management, digital and physical modelling, reporting and presentation. The primary role of the academic staff was
Page 112 LSAA 2007 Surfers Paradise Oct 25/26 Lightweight Architecture Stretching Our Boundaries Internationally to facilitate the design studio environment and to be available to the multi disciplinary teams. At any given time there were at least one architect and one engineer in attendance providing team support. The lectures were given by practising designers from artistic, architectural, and engineering backgrounds. There were also lectures by potential materials suppliers and by sustainability specialists. Students also had access to computing labs, printing facilities, welding and timber workshops and the purpose–designed electronic interface, known as Omnium website (Bennett 1999), which facilitated communication between academics and the student body, as well as communication between team members in a format that encouraged participation without detracting from the studio process. A typical Project X working day (minimum of six hours per day) consisted of a morning lecture, followed by teamwork and consultation in studio. The Interim Jury was held on the seventh day and this Jury comprised the client representative, guest critics, and the four studio tutors. Selected student representatives assisted with the development of the assessment criteria. For the Interim Jury process the students were expected to present a poster, a physical model in site context, and evidence of construction feasibility. A digital model was encouraged but PowerPoint was banned. An exhibition of the work for the Final Selection Jury, which comprised a distinguished artist, architect, and engineer, and non–academic guest jurors, was held on the last day of the course. Figure 1 below shows the winning design and Figure 2 shows examples of other designs. The selected brief was then handed out to students enrolled in Project X2; this course commenced one week after the Final Jury.
Figure 1 The winning design PROJECT X2 Project X2 was offered as a standard once–a–week course in Session 1 2007. The three faculties produced course outlines based on a common agreed model, after agreement on project aims, outcomes, methods of delivery, assessment and the like. The aim was to empower the students to lead the process; to design, fabricate, construct and to manage the project to and to dismantle on time and within the specified budget. To ensure the students’ lead a Student Project Manager (executive student) was appointed. The Student Project Manager was also enrolled in the course. Project X2 included several distinct phases: design development, sponsorship, prototyping and testing, prefabrication and construction, erection and deconstruction. For the first six
LSAA 2007 Surfers Paradise Oct 25/26 Page 113 Lightweight Architecture Stretching Our Boundaries Internationally weeks, during the design development phase, Project X2 was located at the Kensington campus. The teams then moved to the Randwick campus for the prefabrication phase. Once the prefabrication phase was completed, the installation components were transported back to the campus for erection. An academic staff member was engaged as the certifying engineer.
Figure 2 Examples of other Designs MULTIDISCIPLINARY EDUCATION Multidisciplinary project–based courses give students a better understanding of what to expect in the workplace. Project X for example, as discussed by Longbottom et al (2007), provided the following educational elements of multi–disciplinarity: 1. Identity. Each member of the student team tended to take on an identity associated with their background programs. The engineering students behaved as engineers within their group context. Likewise the group members from FBE behaved as architects and the student members from COFA as ’designers’. The students were in a continual role play through the course (Figure 3). They communicated as if they were professionals and were under scrutiny to perform. They also learnt from each other. COFA students witnessed the role of engineering design calculations while engineering students participated in discussions on the fundamentals of the design process, and on aesthetics. It would be easy to exaggerate the openness of these communications. In fact continual effort was needed on the tutors’ part to challenge stereotypical attitudes, sadly already adopted by many of the students. The reach of the project was of course exceptional, from artists to engineers, and staff themselves needed first to address their own preconceptions and attitudes in preliminary discussions, many of which are still ongoing.
2. Responsibility. Beyond cross–disciplinary discussion, team members also needed to perform their assigned role. COFA students would often conceive an imaginative idea which demanded a quick response on practicability from the engineers. Those engineering students who could present their findings in an open rather than a closed manner, assisted their team to progress toward acceptable solutions, rather than having to abandon whole themes.
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3. Individuality. The brief was open–ended and each group devised its own individual solution. There was little scope or incentive for copying, and group members provided original and individual contributions. 4. Innovation/Uniqueness. Having an external jury introduced competition and realism into the course. The winning design as decided by the external jury would be built. The jury process emphasised the need for innovation and uniqueness. The outcome was not predictable. Project X and Project X2 have provided an exceptionally broad and rich multi–disciplinary design learning experience for around a hundred students at UNSW, from a wide range of design–based undergraduate programs. Some students’ comments are included below: ”The course helped me find out how wrong I was for having the impression that artists and designers are weird people that we as normal people can not work with. I found out that they can be smarter than us, ” more normal” than us, and that we had to think a little bit outside the square to get to understand them more” (FE student) ”I learnt the role of each professional area in the design process, encouraging creative thinking and group dynamics.” (COFA student) ”Learnt what designers and architects do. Hands on experience of what it would be like in real life.” (FE student) ”The experience with working in a compressed workshop environment was stressful at times due to impending deadlines, but it was all a good learning experience to plan our time effectively in order to meet these deadlines.” (FE student) ”At first there was less acceptance. But we slowly grow and LEARN from each other. Once we opened up and actually ”see” each others capabilities we begin to learn more. Everyone taught one another something that is not in the textbook.” (FE student) ”This class has helped me develop skills required to reach a consensus. This critical skill I’ll be using in my professional career.” (FE student) ”I even learnt different jargon from the other disciplines.” (FE student) ”Overall in my opinion, this 3 weeks has been really challenging and useful to our future in possible work place.” (FE student) ”I learnt that there’s so much more to engineering than just technical structural analysis.” (FE student) ”Learnt to work in a flexible manner, allowing for changes in the structure throughout my analysis.” (FE student) ”This is more like the real world.” (FE student) ”Good to know how engineers think.” (FBE student) ”Excellent. Working with engineers fantastic opportunity to resolve structural design.” (FE student) ”Every member in the team had something to contribute – surprisingly ideas from engineers were accepted into the design concept.” (FE student) ”The team overall contributes equally to the design. Though there are ups and downs regarding the decision, especially engineering constraints on ”why we can’t build the structure”. But most of the people in the team are open minded and accepts what we have to say.” (FE student) ”The beauty of this project was that although we had a massive task, we also had 4 people working on it, hence lessening the workload.” (FE student) ”As an arch student it was interesting being in between position between design and engineering, motivator, challenging, emphatic, CAD monkey, model monkey.” (FBE student)
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”Everyone in our group worked really well together ”Overall the group worked in an efficient manner, it was challenging for the group to keep a common goal, as students from different faculties wanted to work in different directions. However we managed to keep it all together and work as a team.” (COFA student) ”Although many of us have been complaining about time constraints and not enough guidelines, in other ways it really did push us to our limits and made us learn and grow from it! It’s GOOD!” (FE student) ”Sometimes it was very challenging to explain the whole conceptual process and design development to people who had never come across it before. The explaining time took longer than the time spent talking and generating ideas.” (FBE student)
Figure 3 Multidisciplinary design and construction teams at work STRUCTURAL ENGINEERING AND ARCHITECTURE: HIGHER EDUCATION VS THE WORK PLACE Current barriers and interfaces between engineering and architecture vary considerably from country to country, as do the methods of teaching architects and engineers. The architect has a more diverse education than does the engineer. A typical architectural curriculum covers a broad scope of subjects, both functional and aesthetic. For the engineer, the education is more narrowly focused. The eminent structural engineer, Professor Salvadori, has written: ”A good architect today must be a generalist, well–versed in space distribution, construction techniques and electrical and mechanical systems, but also knowledgeable in financing, real estate, human behaviour and social conduct. In addition, he is an artist entitled to the expression of these aesthetic tenets. He must know about so many specialties that he is sometimes said to know nothing about everything. The engineer, on the other hand, is by
Page 116 LSAA 2007 Surfers Paradise Oct 25/26 Lightweight Architecture Stretching Our Boundaries Internationally training and mental makeup a pragmatist. He is an expert in certain specific aspects of engineering and in those aspects only.” (Salvadori, 1980) Engineers are not commonly perceived as creative professionals. A recent Harris Poll sponsored by the American Association of Engineering Societies and IEEE–USA found that only two percent of the public associate the word ”invents” with engineering; and only three percent associate the word ”creative” with engineering (Stouffer et al., 2004). The creative side of design, especially regarding civil engineering, is commonly thought to belong to architecture. The architect is trained and conditioned to begin the process of design with requirements of the human being, while the engineer is trained and conditioned to achieve a result almost entirely by the application of the principles of mathematics and engineering to problems similarly dimensioned, a process which can in fact suppress the requirements of the human. There is clearly a perceived need by the professions for engineers to be better educated in creative thinking and aesthetic values, enabling them to collaborate positively and constructively with architects and other professionals. Creativity is essential in all branches of engineering and is of paramount concern in engineering design. Yet while ”creativity is an essential component in engineering design”, focused interview with leading creative engineers has found that ”engineering schools do not adequately prepare students for creative endeavours or for the realities of modern industry”. (Richards, 1998) A world–renown Spanish–Mexican architect Candela has written: ”The second design phase consist of a tremendous battle between the engineer and the architect – the former willing to introduce modifications which, although sometimes necessary, many other times should be unnecessary. On the other hand, the architect wants to maintain his preconceived idea, but has no weapons to fight against the scientific arguments of the technician. The dialogue is impossible between two people who speak different languages. The result of the struggle is always the same: science prevails and the final design has generally lost the eventual charm and fitness of detail dreamed by the architect.” (Faber, 1963) Clearly, there is much that the two professions (both play essential roles in advancing human society) could learn from each other when obliged to work together and the best architecture comes from the successful collaboration of the architect and the engineer. The interface between engineering and architecture, therefore, only works if engineers understand what architects do and how they think, and architects understand what engineers do and how they think. (Dickson, 1999) As described by Project X2 students: ”Through the design of the structural system, we have once again seen the contradicting views of design vs practicality. Good design sometimes has to be forsaken because of practical constants. While the engineers and architects do not necessarily speak the same language, it would still be productive for the two to work closely together, if not at the same time as it improves efficiency and smoothens out decision making process. I got a deep understanding about the team work and how important it is to cooperate within a team...” Much has also been written about the need to transform engineering education (Bordogna, 1997) and the apparent disconnect between higher education and the workplace. The modern engineer needs to be educated to thrive through change. No longer do engineers layer directly on traditional disciplines. We all acknowledge that scientific and mathematical skills are necessary for professional success, nevertheless an engineering student must also experience the ”functional core of engineering” – the excitement of facing an open–ended challenge and creating something that has never been created before. In today’s education of structural engineers, for example, there is a strong emphasis on the role of structural analysis at the expense of understanding structural behaviour and synthesis – the art. The development of
LSAA 2007 Surfers Paradise Oct 25/26 Page 117 Lightweight Architecture Stretching Our Boundaries Internationally well–rounded, multi–skilled engineering graduates clearly relies not only on traditional subject material, but increasingly on the development of skills for utilising this knowledge in a creative and innovative manner. The challenge is therefore to make engineering education relevant, to reflect the new market–driven competitive environment, to use technology to enhance learning and to engage the Programs across university Faculties. In addition to being technically competent, engineers must also be creative in problem–solving, perceptive about the global economy, knowledgeable about management, and able to communicate their ideas effectively.
Figure 4 Architect vs Engineer The BE Civil with Architecture Program, hence, introduced for the first time in Australia at the University of New South Wales in 2007, seeks in addition to achieving the objectives of the already existing undergraduate Civil Engineering Program, to address many of the aspects of how a modern engineer should be educated, and to provide an appreciation of architectural principles and an understanding of both the architect’s role in construction and the interaction between architects and engineers. The BE Civil with Architecture Program is not a combined degree; it is a novel cross–disciplinary degree with a major in one Faculty and a minor in another. Because of recent changes to the curriculum structure of engineering degrees at UNSW it became possible to structure a minor stream of courses embedded in the four year core Engineering Program. The Program offers a unique opportunity to integrate engineering and architectural design. Creativity and inventiveness are the key attributes for this Program. It endeavours to close the gap between what is taught in school and what is expected from young engineers by their employers and clients with the ultimate aim to help students become conceptual thinkers, and to develop an appreciation for beauty with the mathematical ability to challenge the traditional boundaries of structural design.
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CONCLUSIONS Project X was designed to provide students with an understanding of the multi–disciplinary processes required for the design of a significant structure, relevant to their other coursework. Project X and Project X2 have provided an exceptionally broad and rich multi–disciplinary design learning experience for around a hundred students at UNSW, from a wide range of design–based undergraduate programs. Together, Project X and Project X2 celebrate both the design process and the education process, both in their multi–disciplinary dimension. ACKNOWLEDGMENTS Project X and Project X2 would not have come to realisation without the lead, support and time provided by Prof. Richard Hough. Sincere thanks are due to all students involved in the project, for their dedication, energy and enthusiasm, as well as to the academic and technical staff involved. Project X and Project X2 were sponsored by FBE, COFA, FE, the ConnectEd Organising Committee, Boral Timber, Visy Board, NRMS, OneSteel, and the Ove Arup Foundation. This support is gratefully acknowledged. LSAA members offered support with supply of PVC coated fabric. REFERENCES Bennett, R. (1999). Omnium [vds]: Presenting an On–Line Future for Tertiary [Design] Education, Outline 99, 17–24. Bordogna, J. (1997). Next Generation Engineering: Innovation Through Integration, NSF Engineering Education Innovators Conference, April 7–8, Arlington, USA. Dickson, M. (1999). Building for a small world–past parallels, future opportunities, Engineering Architecture, Eds. McConnochie et al., Glasgow, UK. Faber, C. (1963). Candela: the shell builder, Rheinhold, New York. Longbottom, C., Bell, G, Vrcelj, Z., Attard, M. and Hough, R. (2007) Project X: Knowing How to Run a Multi Disciplinary Design Workshop, ConnectEd2007 International Conference on Design Education, July 7–9, Sydney, Australia. Richards, LG. (1998). Stimulating Creativity: Teaching Engineers and Innovators”, Proceedings of 1998 IEEE Frontiers in Education Conference, Tempe, USA. Salvadori, M. (1980). Why Buildings Stand Up, McGraw–Hill. Stouffer, WB, Russell, JS, Olivia, MG. (2004). Making the Strange Familiar: Creativity and the Future of Engineering Education, Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition, June 20–23, Salt Lake City, USA.
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A Briefing on European Masters Program & Workshops
Brian O’Flaherty
Presented on behalf of Hochschule Anhalt (FH), FB Architektur, Facility Management und Geoinformation, Dessau, Germany. Information provided by Hochschule Anhalt(FH).
IMS e.V
FB 3 Faculty of Architecture, Facility Management and Surveying Membrane Structures Master Membrane Structures Since the beginning of the fifties of the 20th century numerous buildings were calculated and designed as textile constructions. These textile and pneumatic constructions, cable nets in different sizes and in connection with conventional constructions created a various number of possibilities to build. Compared to conventional construction the shape of textile constructions has to be ”found” with physical modeling or with computational form finding. Therefore it is important to understand the interaction of the physical basic conditions like shape, structure, load, energy and function.
Aim of the study course The lecturers, international specialists in the field of textile constructions, impart knowledge and proficiency to the students so that they are able to design, to calculate, to detail, to build and to keep textile constructions. The special economical and forensic basic conditions will also be integrated. With successful conclusion of the study course the academic degree Master Membrane Structures will be given.
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Admission requirements
H Bachelor or Master degree in Architecture, H Civil Engineering and Surveying, or comparable academic programs of a minimum number of 6 semester study period H at least one year of professional experience H work examples (paper or volume) H certificate of language skills (TOEFL or IELTS is not necessary) Duration of the study course The study course is an international distant learning course which is held parallel to professional life. The lectures will be held in English language only. That’s why interested people from all over the world have the possibility to participate in the master course. The standard period of study is four semester. It consists of three terms each containing one week–long phase of attendance and additional support via internet for the phases of distant learning. The fourth semester is dedicated to the master thesis. Tuition fees The participation in the study course costs the whole amount of 6000 EUR. Schedule of the study course Semester 1 Module 90 minutes lectures Credits attendance home (ECTS) time seminar MM 1 Architecture 9 14 4 MM 2 Numerical Theory 9 14 4 MM 3 Membrane Program 9 14 4 OM 1 Optional Module 9 14 4 Semester 2 MM 4 Structural Design and Detail 9 14 4 MM 5 Mechanical and Physical Properties 9 14 4 MM 7 Project Management 9 14 4 OM 2 Optional Module 9 14 4 Semester 3 MM 6 Dimensioning 9 14 4 MM 8 Internship Theory – Fabrication and Built up 9 Internship 5 OM 3 Optional Module 9 14 4 Semester 4 Master Thesis and Colloquium Thesis 15 Colloquium 2
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Profession The occupational area of the Master Membrane Structures comprises of numerous tasks with the following focal point: H form finding and visualization H structural design and dimensioning H patterning and material requirements H project management and project supervision Therewith the graduates will be able to work in engineering companies which work in the field of membrane constructions.
Contact The IMS e.V. – Institute for Membrane and Shell technologies, associated institute of the Anhalt University of Applied Sciences, is responsible for organization and advice of the study course.
Hochschule Anhalt (FH) IMS e.V. Prof. Dr. Robert Off FB Architektur, Facility Management und Geoinformation Bauhausstrasse 8 06846 Dessau
Study course expert advisor Prof. Dr.–Ing Robert Off E–mail: [email protected]
The application documents you will receive from the IMS e.V. Hochschule Anhalt (FH) IMS e.V. Prof. Dr. Robert Off FB Architektur, Facility Management und Geoinformation Bauhausstrasse 8 06846 Dessau or from the website http://www.membranestructures.de
Request Tel.: 0340/5197–1634 Fax: 0340/5197–3733 E–mail: [email protected] Web: http://www.membranestructures.de
IMS e.V
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Low Environmental Impact Fabric Structures
Pierre Renard (Ferrari) Paul Knox, Innova International i. Scope The presentation aims to demonstrate the positive environmental impacts of lightweight tension structures, incorporating architectural specification membrane fabrics. The environmental performance of a building can be calculated in monetary terms and in BTUs and kilowatts. There is increasing interest in analysing architectural textile options in relation to community impact and sustainability. In doing so, issues arise such as: H Is the material durable? H Is the material recyclable? H Is the material environmentally friendly? Environmental impact can be delineated into 7 major elements: 1. Energy Efficiency
2. Cost Efficiency
3. Design Efficiency
4. Durability and Longevity
5. Solar Protection as Affected by Climate Change
6. Fire Safety
7. Recyclability 1. Energy Efficiency Textile Process Fabrication Installation Reduction in use of air conditioning 2. Cost Efficiency Economy of material use Lower raw material costs 3. Design Efficiency Flexibility Limitless flexibility of form and construction that architectural fabrics offer. The functional and aesthetic needs of a project design within lower budget parameters can be met with these very tailorable fabrics. Compared to higher impact conventional construction materials, fabric clad structures offer the prospect of curvilinear 3 dimensional creations that are also inexpensive in relative terms.
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Low impact tension membrane structures release elements which are evolutionary in their ability to alter the built landscape. What an exciting community or environmental dimension to use these structures to orchestrate change from hard, sharp surfaces and forms using cold, inorganic materials to forms which flow. To modify our environment prosperously away from the primacy of linearity. Renowned Swiss architectural firm Herzog & de Meuron state as their ethos ”Architecture has to be sensual and intelligent, otherwise it is boring”. 4. Durability and Longevity Subject to appropriate selection criteria architectural textiles are highly durable (sustainable) and long living. 15–20+ year life spans are increasingly common with the technology available from specialist textile mills. 5. Solar Protection / Climate Change Designers will increasingly be challenged to find more passive means to cope with hot, dry climates rather than run with the seemingly unstoppable application of high energy consuming air conditioning systems. 6. Fire Safety Architectural textiles range from non combustible (PTFE) to low combustability (PVDF/PVC). 7. Recyclability Harvesting of raw materials for re–use. Easily demountable material. Light weight and easy to transport. Example The Arizona based Sonoran Institute, a non profit organisation, has as its focus the creating of ”lasting benefits, including healthy landscapes and vibrant communities”. Last year, and Arizona USA Green Building Award was won by the Edith Ball Aquatic Centre in Tuscon. An architectural fabric was used in a classical ridge supported form that served as a large umbrella covering lap, recreation and wading pools and surrounding deck areas. In summer, the fabric structure shades a larger portion of the pool and deck from the higher overhead sun. In the winter, the longer southerly sun penetrates deeper under the fabric membrane edge providing a large sun bathing area. The most significant energy and resource conservation aspect of this project was the decision to abandon the original plan of placing all of the pools in mechanically conditioned enclosed interior spaces. This accomplished initial construction cost savings and will achieve a substantial operation and maintenance saving over the life time of the facility. FAS Arch, July/Aug 2006
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Wind Engineering for Lightweight Structures
A.W. Rofail Windtech Consultants Pty Ltd, Sydney, Australia
1. INTRODUCTION Lightweight structures are by definition wind–sensitive. This is particularly the case where spans become very large or where the structure is supporting large areas of lightweight panels or fabric. Hence the structural design of lightweight structures becomes dominated by the design wind loads. Structures that would fall under the category of lightweight structures include but not limited to: 1. long–span cable–stayed or suspension bridges 2. long–span or cantilevered roof structures (such as for large warehouses or stadiums) 3. special structures such as large roof fins, large screens & signposts or large clad sculptures This paper presents an overview of the techniques employed by leading wind engineering consultants in providing accurate estimates of the wind loads for such structures. The emphasis will be on the second and third items, which have benefited by new wind tunnel testing techniques. These new techniques that have come about over the past decade or so are now possible due to advances in both signal processing and computer capability. These have significantly improved the reliability and accuracy of the wind load predictions. With the increased accuracy has come a significant increase in both cost efficiency and robustness of the structures that are amenable to these techniques. 2. HISTORICAL OVERVIEW The failure of the Tacoma Narrows Bridge due to aerodynamic effects in 1940, only 3 months after commissioning, lead to the recognition of the need for proper study of the dynamic response of such lightweight structures to wind. After an extensive investigation involving wind tunnel modeling performed in Canada, it became evident that the failure was a result of a resonant response in the second torsional mode with the frequency of vortex shedding generated by the subject bridge deck form. It was not until the mid–sixties that wind engineering began to merge with the engineering of tall building structures. Wind engineering became recognised as a discipline in 1970. The techniques used for modeling the complex behaviour of strong winds over the earth’s surface in terms of their structure and turbulence have not changed much since the 1970’s. However, the techniques for measuring and analyzing the effect of the wind on the structure have changed significantly over that period. These changes have not affected the techniques for modeling the wind effects on bridges as much as other types of structures such as stadium roofs, special structures and even tall buildings. There are now much more sophisticated techniques that allow us to know a lot more about what the wind is doing to the structure and enable us to model much more complex structures than was previously possible. Complex structures can be either in terms of their form or their dynamic behaviour (or both). It turns out that these techniques have an added benefit in that the resulting loads for some structures tend to be substantially lower than was previously thought due to the effect of low correlation of the peak pressures across the structure. Stadium
LSAA 2007 Surfers Paradise Oct 25/26 Page 125 Lightweight Architecture Stretching Our Boundaries Internationally roofs are an example of such structures. This paper discusses the methodology, background and application of the pressure correlation technique with examples. It also discusses how the modeling of the effect of wind on some unusual structures is possible. 3. PRESSURE CORRELATION TECHNIQUE The pressure correlation technique was developed by Dr Michael Kasperski (Germany) and Dr John Holmes (Australia) about 15years ago (Kaspeski and Niemann, 1992 and Holmes, 1992). This technique is applicable to structures where the dynamic component of the structural response predominantly consists of the background component of the response and there is little chance of aerodynamic damping effects. Structures that fit into this description are stadium and long–span roofs as well as any canopy or large roof–fin structure. This technique is also applicable to quasi–static structures, where the form is relatively complex such that the use of wind loading standards is not possible. This technique requires the use of the simultaneous pressure measurement technique (in real–time). The entire surface of the structure is pressure–tapped and the pressure signals measured simultaneously. The importance of having the pressures being read in real–time (minimal phase lag between the various pressure taps) stems from the need to accurately determine the following: H a pressure correlation matrix, representing the relationship between the pressure signal at different areas of the building surface H the various load effects, which are determined by area–weighting the pressures from the different areas (pressure integration) It is important that the structural engineer carefully selects the various load effects that are to be monitored as these will determine the load cases that would be used to design the rest of the structural elements. Hence the load effects need to be for key structural members from different parts of the structure that are sensitive to pressures from the different areas of the building surface. In some cases it would also be helpful to determine different types of load effects such as displacement, shear force, axial force, bending moments (about different axes) for the same member. For quasi–steady structures, the only input required by the structural engineer is a pressure correlation matrix. A stadium or long–span roof structure is considered quasi–steady if the first natural frequency is greater than 0.8Hz, whereas a vertical structure such as roof fin is considered quasi–steady is the first natural frequency is greater than 1.2Hz. A pressure correlation matrix determined by first dividing the envelope of the structure into a number of patches. There are typically between 30 and 60 patch areas for a stadium roof structure. The patch roof is divided into patches in line with areas that would be expected to have different range of pressures for the same wind direction (such as due to surface discontinuities or for aerodynamic reasons, such as wall or roof edges). Each patch consists of a number of pressure taps that are area averaged. A pressure correlation matrix is determined by applying a unit pressure (such as 1kPa) normal to the surface of one patch and then read out the reactions for each of the key load effects that are being monitored. This would provide the data for one row of the matrix. The process is then repeated for the next patch area and so on.. For structures that are likely to have a significant resonant component, the following additional inputs are required from the structural engineer for the various modes that have natural frequencies less than 0.8Hz in the case of a stadium or long–span roof or 1.2Hz in the case of vertical structures such as roof fins:
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H the natural frequency and mode–shape for each of the applicable modes of vibration. The mode–shape is normally expressed in the form of the displacement at the middle of each patch, normal to the patch surface. H The mass and area per patch This additional information is required to determine a generalised force for each of the load cases being monitored. This generalised force is then analysed spectrally to determine the prototype response of the structure. Usually the resonant response will comprise no more than 10 to 20% of the peak values of critical load effects and this contribution can be calculated separately and added to the fluctuating background response using a ’root–sum–of squares approach’. The effective static load distribution corresponding to each peak load effect can then be scaled up to match the recalculated peak load effect. When the resonant response is more significant, the inertial loading from the resonant component is correctly combined with that from the direct wind pressure, by a weighted summation (Holmes, 2002). The advantages of this technique can be summed up as follows: H no limitation to the complexity of the structural behaviour as there is no need to model such structures H More accurate information regarding the critical load combinations between the various patches taking into account the effect of correlation of pressures across the structure H an ability to accurately determine any number of load effects directly, without having to make assumptions regarding pressure distributions H more accurate than traditional aeroelastic model techniques, which are limited in their ability to accurately model the dynamic behaviour of the structure and provide little guidance in relation to critical load cases H the technique is more cost effective and requires less time that the traditional technique, provided that the computers can be effectively mobilized to perform the extensive data analysis required 3.1 CASE STUDY 1: GOLD COAST STADIUM A study of the wind loads on the structure and cladding for this stadium was commissioned by SKM and Tensys as part of a value engineering exercise to meet tight cost constraints. A wind tunnel study was carried out on a 1:150 scale model of the stadium. A model scale as large as 1:150 was required to ensure correct simulation of the flow regime around the curved surface of the stadium roof, due to Reynolds Number effects. A photograph of the model in the wind tunnel is shown in Figure 1. The pressure correlation technique was used in analysing the wind loads on the structure. In addition, a number of options were investigated to alter the roof edge configuration with a view to further reduce the wind loads. It was later decided not to modify the roof edge configuration. The entire envelope of the roof structure was divided into 64 panels. Each panel was pressure tapped on both sides using between 4 and 8 pressure taps per panel. Pressures on the entire roof structure were measured simultaneously to derive a correlation matrix as well as to determine time series of the generalised forces to determine the peak responses. A total of 15 load effects were monitored for maximum and minimum responses. These include 6 bending reactions, 6 axial loads, 2 tip deflections and 1 pile reaction. The
LSAA 2007 Surfers Paradise Oct 25/26 Page 127 Lightweight Architecture Stretching Our Boundaries Internationally corresponding 30 critical load combinations were rationalised to 24 load cases. The maximum 100year return patch pressure was approximately 2kPa represents a substantial reduction over the estimate by AS/NZS1170.2:2002. Furthermore, the effect of the correlation study is such that it significantly reduces the incidence of large pressures on more than a couple of patches at a time in a given load combination. In the study of the wind loads on the cladding, area averaging was used as the cladding consisted of a tensile fabric. This approach resulted in reductions in the design loads for the cladding of the order of 20% over the measured point pressures. The maximum 10year return panel pressure was around 2kPa, which represents more than 40% reduction over the estimates in AS/NZS1170.2:2002, even with the effect of the area reduction factor of 0.80. This is significant reduction in the loads is largely attributable to the curved, aerodynamic form of the roof. 3.2 CASE STUDY 2: NANJING STADIUM This was the main stadium used for the 2006 China Games. This stadium roof structure consists of a perimeter truss support as well as cable ties supporting the end of the cantilever by means of overhanging arches (see Figure 2). This relatively complex structure would be virtually impossible to model using the traditional aeroelastic modeling technique. Windtech Consultants were engaged by SKM to perform the wind tunnel study for this structure. An accurate 1:300 scale perspex model of the structure was prepared using the computer–aided rapid prototyping process, as shown in Figure 3. This scale is more than sufficient for modeling of Reynold number effects for this structure. The entire envelope of the structure, including the overhanging arches was divided into 64 panels as shown in Figure 3. A total of 512 pressure taps were distributed over the entire surface of the roof structure and simultaneous pressure measurements were performed over the entire structure. A total of 15 load effects were monitored for one quarter of the structure to take advantage of the double symmetry. The load effects consist of a mid–span displacement, 5 moment reactions and 9 axial loads. The maximum and minimum load effects resulted in 30 critical load cases, which were rationalised down to 8 load cases as shown in Figure 4. Note the difference between the instantaneous peak patch pressures required based on the pressure correlation technique in comparison to the maximum and minimum pressures derived from a simple discretised area–averaged patch pressures indicated as solid lines in Figure 4.
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Figure 1: The 1:150 scale model of the Gold Coast Stadium in Windtech’s Boundary Layer Wind Tunnel.
Figure 2: A perspective image of the Nanjing Stadium
Figure 3: The 1:300 scale model (left) and a diagram showing the different patch areas (right)
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Figure 4: Discretised panel pressures (Max and Min) versus the 8 load cases for Nanjing Stadium The natural frequencies for the first 5 modes were 0.75Hz, 0.77Hz, 0.79Hz, 0.81Hz, 0.95Hz. Hence in addition to the pressure correlation technique, a pressure integration method was applied to analyse the resonant response from the first four modes of vibration. For this structure, modes higher than the fourth mode would have a negligible contribution to the resonant response. The results of this analysis indicate that the resonant component of the response has a maximum additional contribution of 10% to the total dynamic response. 3.3 CASE STUDY 3: CAULDRON FOR ASIAN GAMES 2006, DOHA This complex structure consists of 2 slim rotating rings that revolve around a main ring located on a 25m high shaft. This is a temporary structure and is intended to be in place for about 4 months from December 2006. A 1:50 scale model of the structure was prepared using the rapid–prototyping technique, as shown in Figure 5. This model was placed within a 1:50 scale model of the Khalifa Stadium. A model was also configured with pressure taps within each ring and over the supporting shaft to enable the use of the pressure correlation technique. The model was designed such that the rings can be rotated to simulate the effect of different stages of the rings’ revolution relative to each other and for the erection mode configuration. A total of five ring configurations were tested. Before commencement of testing, a study was carried out using a 1:300 scale model of the sports precinct to determine the effect of the surrounding structures on the upstream velocity and turbulence intensity profile for wind incident from different wind directions. These wind profiles were replicated at 1:50 scale to be used for this study. Also an extensive analysis was carried out of the wind climate for Doha. This included a seasonal extreme wind speed analysis to correspond with the time of year when this structure is to be in place. Fortunately, the December to April season co–incided with the most benign season for extreme winds in Doha and therefore a lower design wind speed was adopted. For each of the five ring configurations, two wind tunnel testing techniques were performed: H high–frequency force balance H pressure correlation technique
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The high–frequency force balance technique was important as a check on the results of the pressure correlation technique. The need for the pressure correlation technique stems from the need to determine the relative displacements of the ring elements, as they need to operate within very strict limits to avoid the rings colliding into each other (there is only a few centimeters gap between them). The pressure correlation technique is also useful in providing a more accurate set of equivalent static loads for such an unusual structure. The results showed that the value of drag from the pressure correlation technique was about 20 percent higher than those obtained using the high frequency force balance. This is due to complexity of the form of the structure and the curved form. Nevertheless it provided an acceptable level of confidence in the predictions.
Figure 5: The 1:50 scale model of the Cauldron for the 2006 Asian Games, Doha. Left: On the force balance before inclusion of the Khalifa Stadium section model. Top Right: Within a section of the Khalifa Stadium and using the pressure correlation technique.
4. TECHNIQUES FOR POROUS STRUCTURES The modeling of porous screens requires special care. Where a screen consists of elements of circular section Reynolds’s Number effects can be significant. The Reynolds Number is a non–dimensional number that is proportional to wind speed and scale. The flow regime around bluff bodies varies with different Reynolds Numbers. Flow around Circular Cylinders is particularly sensitive to Reynolds Number. In some cases the only way to accurately model the drag of such screens is to artificially enlarge the diameter of the cylindrical elements such that the flow around them in the wind tunnel is operating under the same Reynolds Number Regime. For net–type screens with a relatively even porosity, our research shows that the porosity of the wind tunnel model of the screen will need to be increased by a certain factor to provide equivalence in the value of the drag.
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4.1 CASE STUDY: LED SCREEN FOR ASIAN GAMES 2006, DOHA Windtech was engaged by SKM to investigate the wind drag forces on this 150m long and 58m high porous screen. This screen consists of a matrix of LED screens connected via 25mm diameter vertical cables. The screen was used for the opening and closing ceremonies of the 2006 Asian Games in Doha. The aim is to determine the amount of wind drag for which to design the supporting structural frame, which consists of a series of 8 vertical space trusses. To be able to model the effect of the Khalifa stadium on this structure, a scale of 1:300 was required. However, to be able to model the flow regime around the cables the scale of the cables was exaggerated by 60 times relative to the model scale (1:5 scale). This was to ensure similarity of flow regime between the model and full–scale.
Figure 6: The 1:300 scale porous model of the LED screen for the 2006 Asian Games, Doha connected to the force balance.
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Figure 7: The 1:300 scale impermeable model of the LED screen for the 2006 Asian Games, Doha connected to the force balance. The model was attached to a force balance and was tested with two configurations: a porous screen configuration as shown in Figure 6 and an impermeable screen configuration as shown in Figure 7. In addition the drag on the force balance shaft alone was also measured and he drag subtracted from the two measurements. This enabled the determination of the porosity factor for wind from different wind directions. An example of the results (for the main axis) is as shown in Figure 8.
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Figure 8: Drag Coefficient Comparison between the Impermeable and Porous Screen (along the East–West axis) Note that the results for wind from the critical west direction are somewhat affected by the presence of the Khalifa stadium structure. The pressure tapped model was then used to provide an accurate distribution of the loads between the 8 panels areas that correspond to the 8 supporting space trusses (refer to Figure 9, below). A photograph of the pressure tapped model before inclusion of the Khalifa Stadium model is shown in Figure 10. The test using this model was also used as a check on the results of the force balance tests using the impermeable screen option.
Figure 9: The tributary areas for each supporting vertical space frame structure.
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Figure 10: The 1:300 scale pressure–tapped impermeable model of the LED screen for the 2006 Asian Games, Doha. REFERENCES: Kasperski, M. and Niemann, H.–J. (1992) The L.R.C. (Load–Response–Correlation) method: A general method of estimating unfavourable wind load distributions for linear and non–linear structural behaviour, Journal of Wind Engineering & Industrial Aerodynamics, v.43, 1753 1763. Holmes, J.D. (1992) Optimised Peak Load Distributions, Journal of Wind Engineering & Industrial Aerodynamics, v.41, 267–276. Holmes, J.D. (2002) Effective static load distributions in wind engineering, Journal of Wind Engineering & Industrial Aerodynamics, v.90, 91 109.
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Lightweight Structures – Where We Have Come from and Some Current Issues
Dr Peter Kneen EO, LSAA
Introduction This paper is a recollection of personal and industry developments for lightweight structures over the past forty years. During this time, some great technology advances have occurred whilst other issues have essentially remained ”on the table” and require further debate. My early ambition was to be a hybrid architect / engineer after the great Italian Pier Luigi Nervi who designed and built many large span roof structures in which the pure structural form was exposed. Many of his structures were constructed in concrete. To this day, I have not designed a lightweight concrete shell so I have fallen short of my original goals. Nervi carried out optimization processes to minimize the use of material, or to maximize the benefits of having an appropriate three dimensional shape. Spaceframe Structures Mt Feathertop Dome Aluminium was my first lightweight material and a small 6.5m diameter geodesic dome my first project completed in 1966 on Mt Feathertop in Victoria. It is both a memorial hut for the Melbourne University Mountaineering Club (MUMC) and a refuge hut for hikers and winter expeditions. It just survived the devastating 2002/03 bushfires. The upper sleeping floor is suspended from the geodesic dome and the log book has recorded over 30 occupants on a number of occasions.
All materials including red gum posts, timber flooring, cement and sand were carried in by hand from as far away as Mt Hotham or up the 1250m climb from the Ovens Valley along the new track constructed by the MUMC. The final dome diameter was determined by the width of the flat sheets (0.6mm thick) of aluminium cut into triangles to form the skin. These were designed to act as a membrane between the recticulated aluminium RHS. All frame members were cut to length by students of the MUMC. The custom designed joints were also cut and drilled by the students from aluminium sheets. The dome was assembled joint by joint using a theodolite positioned at the centre of the sphere to give the correct angular location – the radius being measured with a tape. All calculations were done using a slide rule and there were no engineering drawings other that sketches of the various components.
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There were fire requirements to be met – as prescribed by the National Parks authority – with several of the lower windows offering an alternate escape route and tomahawks placed on the upper level to hack through the top sky light if necessary. Today the hut remains in excellent condition but shows the effects of the bushfires which burnt to within 0.5m of the surface. The hut was saved by helicopters dumping fire retardant on the roof. Exhibition Building Sao Paulo The next aluminium structure in 1968–69 was a bit bigger – in fact the largest Aluminium structure in the world. It is the exhibition building in Sao Paulo and measures 260 x 260 metres. It is a double layered two way spaceframe using tubes approximately 3.33m long. The ends of the tubes were flattened and bolted to a cruciform welded steel plate joint. The complete roof was assembled at ground level and lifted in one operation. Umbrella type supports were used (a simple ”tree”) at 60m spacing for the inner spans and 53.3m outer spans. These umbrella supports sat atop bipeds which were orientated perpendicular to a radius from the central fixed point. Thus, the considerable thermal expansion could take place without restraint but the plurality of differently orientated bipeds would combine to resist horizontal wind loads from any direction. In terms of the technology of the day, the analysis of the roof with some 48,000 tubes and over 12000 joints was a challenge. The existing method for analysis of flat spaceframe roofs was to replace the frame with an equivalent plate and to use plate or shell theory – generally in the form of published coefficients for shear forces and bending moments. Timoshenko had written the classical works in these areas. However, when unusual support locations and boundary shapes were present, there were no accurate solutions. The ”matrix theory” for structural analysis of frames was known and some software programs such as SAP (Berkeley) and STRUDL (MIT) were starting to appear. These appeared to be the way forward as the actual frame and support conditions could be accurately modelled. Conceptually, the theory was easy – a set of equations P=KD would be formed in which D was a vector representing all the unknown joint displacements, P the applied load components on those joints and K the stiffness matrix describing the structure elastic properties. Personal computers were still some time off and the number of computers available was very limited. Computer memory consisted of tiny iron rings with electrical wires passing through – a current would produce a magnetic field in the rings which was interpreted as a 0 or 1 – a ”bit” of information. Eight of these rings would be combined into ”bytes” and then four of these ”bytes” into a ”word” which was sufficient to represent a single precision real number. At the time of this structure, the largest computer available (the 2nd largest in Canada) shown below had a total memory of 4Mb of which at most only 1Mb was available by special arrangement and normally only 256Kb was allocated. This 256Kb had to include the machine language version of the program as well as any data that was needed. For the roof, the stiffness matrix K could have some 1,400Mb worth of (single precision) numbers to store. Virtual memory was not around either and the scientific programming language was Fortran (which is still used today). All input was done using punched cards (these had displaced punched paper tapes in the early 1960s). Dumb terminals didn’t appear until the late 1970s. How was this structure solved? By careful use of symmetry of the structure, several representative sections of the total roof were analysed. A small Fortran program was developed for the project and most of this development went into refining the methods for solving large sets of banded simultaneous equations. Several bugs were found in the Fortran compilers and computer operating system during this project. Subroutines were written to generate the data but the listed member forces were processed manually and new tube sized determined. The revised structure was reanalysed. Some months afterwards, the members
LSAA 2007 Surfers Paradise Oct 25/26 Page 137 Lightweight Architecture Stretching Our Boundaries Internationally were selected by the purpose written software – one of the first applications of ”computer aided design” as we know it today.
Victorian Arts Centre Spire The next major Aluminium (in part) structure designed was the spire for the Victorian Arts Centre in the mid 1970s for Sir Roy Grounds and John Connell & Associates. The lower ”skirt” comprises four complete hypars and eight truncated hypars subdivided into 16 parts with diagonal members in the shortest direction. The Triodetic system was used for the lower shells which involved extruded slotted hubs as joints into which coined tubes were inserted. This coining process meant that each member had virtually no bending strength about one axis but full strength about the other. Each joint was orientated normally to the surface of the hypar which meant that there was a ”twist” angle associated with each member. Since this would impact on the distribution of forces, it was necessary to describe each member more accurately than simply connecting two joints. In terms of computer technology available at the time, the UNSW had a Cyber 72 and the ACES structural analysis program developed in South Australia. Virtual memory was available but from my recollection, the computer had to be restarted especially. As a result, one could only do one or two runs per week for large analyses. A special ”pre–processor” program was written which could generate the input data for ACES. The input format reflected the punched cards used. Advances now included being able to store this information on a disk file rather than physically carry boxes of cards all the time to the input station. However there were only a handful of computers for the entire University so it was a drawn
Page 138 LSAA 2007 Surfers Paradise Oct 25/26 Lightweight Architecture Stretching Our Boundaries Internationally out process. It was a ritual to make the journey to the computer centre to pick up your input cards hopefully surrounded by a nice thick bundle of paper to pore over for the rest of the day. Then to find a card punch machine that was free (and well adjusted – those punched holes if misaligned could mean the job would fail). One had to be very careful typing in the data – once a hole was punched, it could not be repaired – a new card was needed. Anyway, the structure got analysed okay and the printouts sent by courier to Melbourne so that a design check of every member could be carried out. It was not long before a plea came back to see whether the computer could somehow do this. Well, there was no documentation on how ACES stored data on disk – all we had was the output file which fortunately we had copied onto a magnetic tape. A ”post–processor” was written which essentially had to read the printout page by page, skipping headings, page numbers etc until the appropriate results were found. Then these were compared to the design codes and appropriate pass/fail flags set along with stress summaries for each load case. The structural analysis of the shells was a linear elastic analysis of each shell acting independently from each other – there were really no readily available tools to perform a large displacement analysis or to model aspects of joint tolerances. The project also required modifications to the manufacturing process and part of the work involved producing a reasonable sized prototype of one of the truncated hypar shells. All the tube lengths, end coining angles, bend angles and hub dimensions were calculated and the 1500 tonne hydraulic press was modified to be able to correctly produce tubes to match. The purpose of the prototype was to confirm all these changes but in addition it was used to carry out a load test. There was some available knowledge of complete hypars but none of truncated hypars. What degree of edge stiffening was needed and what influence was the lateral stiffness of the supporting edge beams were unknown.
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The structural testing involved some basic technology as well as pushing into new areas. The basic technology was to manually add bricks to simulate increasing loads applied to joints. Strain gages were used on a selection of members with some primitive data collection equipment. The more advanced technology was to use photogrammetry to attempt to measure the joint deflections and rotations. A high quality camera was mounted on an overhead crane which was moved between two positions at each load increment to give the stereo images required. Special cruciform targets were attached to each joint. The down side of this was the amount of manual effort required to use expensive equipment to measure the positions of the targets from the films. The geometry of the upper spire was designed from a background of work with polyhedron and studies of redundancy in structures in 1965 and 1970 with Professor M Burt. It was my first application of geometric non–linear analysis and the simulation of material (member) failure and manufacturing imperfections.
Studies of infinite polyhedra and minimal surfaces with Prof Michael Burt in 1970
Design documentation in those projects was still done manually on the drawing board and by fabricators later for the shop drawings. Revised sets of drawings were delivered by couriers across the country and storage and retrieval of correct drawings were a problem. Telephone conversations involving examining different drawings was a problem (speaker phones in the future still) so there was a tendency for more face to face meetings than is required today. Ah – the aroma of ammonia from the print rooms! There was little in the way of standards used for exchange of information. Gradually information appeared in one place – such as on the architectural drawings for column spaces, layout grids, floor to floor RLs and so on. Beam and column sizes would be on the structural drawings which would have sets of typical details and specials. To produce the final set of shop drawings, the detailers would need to gather information from several sources and by the time this was done there might have been changes made which were overlooked. The shop drawings may have been subsequently checked by the engineer who may have moved on to a new project. The real checks came on the job some considerable time after the design was developed. Contractors would make their money because of variations and delays whilst missing information or rectifications were worked out. The dreaded RFI. We will revisit the current situation later in this paper.
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Membrane Structures Bernie Davis is credited with designing the first significant (other than several pneumatic structures) tension fabric structure in Australia which was closely followed by the Dean Park Sound Shell in Townsville in the late 1970s by Geodome Space Frames. Dean Park Sound Shell A fixed price contract had been signed with the client which covered all engineering design as well as supply and erection of the sound shell. As there was no software in Australia, the suggestion was to approach one of the established overseas consultants to perform the design. No – problems. Pay up front approximately 15% of the total contract for a preliminary structural design of the supporting structure. Add to this the unresolved patterning needed and detailed design of connections suggested that we had to develop our own technology. The client was supportive and permitted a generous extension of time. A small 1:100 scale model was constructed. On the computer side, an approximate 3D shape was generated using the technique of isoparametric shape functions from the finite element method to model a mesh over a quarter of the surface. This mesh was triangulated and flattened out into strips. The strips were not related to actual fabric roll widths but were used to create a 1:10 scale model using lightweight spinnaker cloth complete with pockets for edge cables. A guess was made at compensation factors for the final PVC coated polyester fabric. By stretching the model, some slope discontinuities along lines of symmetry were ironed out. An iterative structural analysis program was written in an attempt to simulate the behaviour under wind. The analysis did move in the right directions but failed to converge so an approximate hand analysis was done.
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From what was known, an initial prestress in the fabric of 1 kN/m was assumed and this was translated into a calculated tie down force at the two low points of the structure. A reasonably clumsy arrangement was used at these tie downs which allowed for all sorts of adjustments. A hydraulic jack was inserted and used to impart an 86kN load. Threaded VSL bars took over after the jack was removed. Fortunately, the surface felt uniformly taut and subsequently performed well for the life of the structure. Queen Street Mall, Brisbane The next major structure was two inverted conical umbrella structures in Queen Street, Brisbane in the early 1980s. A HP85 small computer was available with 32Kb of memory. An approximate shape generation procedure had been programmed using the Basic language and considerable progress had been made in the patterning so that it was no longer necessary to construct a large scale physical model to measure up for the patterns. The form finding of these and several other conical structures was done by eye without any soap film or simulation of a stressed condition. A major step forward in this project was the first known use (by Bullivants at least) of the threaded swaged end for edge cables. This meant that reasonably compact connections could be designed.
Major software developments were happening overseas by Birdair. A VAX computer with a graphical monitor was being programmed by consultants from the emerging computer graphics area. It was possible to define a number of key points (on the monitor) and generate a suitable mesh. This program is now available as MCM–lite. In Europe, the finite element programs were being used extensively and software by Prof. Lothar Gründig developed for the form–finding and analysis of the Munich Olympic Stadium cable net roofs has since evolved into the Easy program and latterly the Technet program in
Page 142 LSAA 2007 Surfers Paradise Oct 25/26 Lightweight Architecture Stretching Our Boundaries Internationally the 1990s. In the UK, the ”dynamic relaxation” method was refined by Barnes at Bath which has evolved into the Tensys program. The form–finding process for the Munich Olympics was supplemented by elaborate physical models. An earlier cablenet was designed for the German pavilion at Expo 67 in Montreal and a smaller prototype structure was constructed at Stuggart which forms the home of the Lightweight Structures Institute (IL). The IL was the source of much of Frei Otto’s work. Many students were attracted to the IL including Prof Vinzenz Sedlak the founder of the MSAA which later became the LSAA in Australia (see above picture with his model of the demountable stage for the Sydney Festival). A lot of the early work of the IL involved models of soap films and minimal surfaces. Soap films can be a brilliant starting point for tensioned fabric structures and have been incorporated into software packages. Unfortunately some forms such as high–rise cones give rise to crazy soapfilm shapes and forms that involve non–uniform stress distributions had to be used. The concept of having geodesic strings floating around within a soap film was utilized some fifteen years ago. The idea was that the triangulated mesh could be pulled into the shortest lines across a surface. When used later for patterning, it was thought that these geodesic strings would produce the straightest strips of fabric and maximise the use of material. Computer Modelling of Materials Several software programs were developing more complex elements to model the material. Thus a layered material having a homogeneous base representing the coating and two separate disconnected layers of yarns for the warp and weft fibres was found to behave more realistically that a simple elastic material. In addition, these layers of fibres could be defined so that they could not resist compression. Cable elements that could be defined with prestress or initial strains and being tension only started to appear in general purpose finite element packages in the early 1990s. Packages were also performing large displacement analyses with geometric stiffness matrices for common structural components. The ability to handle different contact problems also assisted the fabric structure industry. Now it would be possible to simulate the sliding of a fabric sheet across a supporting arch, or to permit the fabric to lift off from a support under wind loads. Of course, there still remain some computational areas awaiting development. These are related to better refinement of material modelling under biaxial stress conditions including localized wrinkling and the crimp interchange behaviour first mentioned in the 1980s. It is still an industry issue to obtain realistic data on fabric behaviour – both short and long term. Great advances have been made in the simulation of composite materials such as carbon fibre and resin.
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Modular shade structures using seat belts for edge cables and knitted shade cloth were developed by the writer and have become industry standard. Above is the large deflections due to hail loads and on the right an Award winning conical structure designed with planar panels and the flexibility of the shade cloth material (Green Scene, Victoria)
Computational fluid dynamics is a field that could be applied to free form structures to obtain a better understanding of wind pressures, external turbulence as well as internal air flows, heating and cooling loads and lighting requirements at different times of day and seasons.
Expo88 in Brisbane was a major project designed by European Engineers. Australian Companies constructed several elegant smaller structures.
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The MSAA / LSAA sponsored some wind tunnel tests on a range of conical surfaces Computer Technology – Communications and Data Interchange Standards Great advances in computer technology have been taken up by every professional. The use of email for instance, when combined with the ability to send all sorts of files as attachments (drawings, photos, spreadsheets, data files, manufacturing data etc). The Internet has enabled communication and design/construction development to be a world–wide 24/7 operation because of the different time zones. There is no doubt that the Internet is a vital element in the ability of Australian / NZ designers and contractors to be able to tackle overseas projects. The other area which is still improving is in the adoption of various ”open” standards for electronic data interchange. This is when, for example, a CAD application may generate geometric information which in turn can be read or transferred without loss of attributes into another application such as a structural analysis program. An early attempt was the IGES standard which was adopted by several software companies originally for the exchange of information such as might be needed for a finite element analysis of a structure. This standard didn’t really get off the ground as it was realized that so much more intelligence needed to be associated with the myriad of potential data that is needed to describe a product or structure. In the early days, a beam might simply have a section size specified (610UB101) which would be enough to locate the geometric properties needed for an analysis. Now, we might also add in connection types at both ends, position and types of added stiffeners, cut outs, shear studs, material grade, supplier, paint or surface finishes, centre of gravity for lifting purposes, required delivery times and so on. Obviously a structural analysis package will not need to know about the paint finish but will need to know the geometric properties and ideally the stiffness properties of the end connections. A package needs to get what data it needs from a centralized data base for the structure but also leave other data intact. Many packages now are able to perform a design check of members against local design codes and may offer the ability to automatically select alternate member sizes to meet the design criteria. Such changes will cause a ripple effect such as changing surface areas, self weight, costs and so on.
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The industry, which is often being driven by software companies, is working on open standards to permit the above types of data storage and interchange. More and more information is being generated and is kept basically in one database or model. Terms like intelligent 3D or 4D model or BIM are common now. Yes, time is the fourth dimension as a structure doesn’t miraculously appear. It is a growing requirement that structures are assessed for all major stages of construction and the centralized database needs to be able simulate the stages of construction. This is a great bonus for erection planning and transport requirements including loading, unloading and on–site storage needs not to mention craneage. In the past, after a structure (building) was completed, the original drawings were modified manually to become an ”as constructed” set of documents, copies of which were handed over to the clients. Ongoing maintenance and alterations throughout the life of a building (new partitions, stairs, services etc) somehow just happened. Now, the developed 3D or 4D model is handed over and can be used throughout the life of the building. It may well be available so that fire departments can predict which evacuation or fire fighting techniques might be used in emergencies. This is a far cry from the days when a bundle of computer punched cards was the only static representation of the building for a brief moment in time. In the past, we relied very heavily on the 3D thinking skills of structural detailers to visualize what was going on and to represent the various components on the drawings. The early CAD systems were simply a 2D drafting tool to replace the pens, T squares and scales of the drawing office. What was drawn was still controlled by the operator. The later stages of documentation (the shop drawings) collated all the bits and pieces together and final costs could be established. Unfortunately cost estimates and contract prices needed to be determined early in a project before final details were determined. In the field of tension membrane structures, it was soon learnt that connections of cables for example had to consider large variations in geometry from the initial attachment of a loose cable to a mast right through to when the structure has been stressed. Corner connections in fabric structures visually demonstrate the relative forces meeting at a point. More traditional structures modelled in 3D can be examined for access of spanners and wrenches to insert and do up bolts for example. This is called clash detection which originated in structures such as refineries where pipes and other services must avoid each other. Structural engineers were often upset when the architectural requirements demanded that air conditioning ducts had to pass through our carefully optimized beams. All the other pipe work in buildings (water, gas, electrical, communications) had to somehow get around our structure and didn’t show up on our drawings. With the present situation, all this other information can be absorbed into the same 3D/4D model. This poses a small procedural problem in that we don’t want unauthorized people being able to stuff things up – say by altering some pipe locations that then pass through a beam or column. Thus a system of data organization and access is an inherent part of the models. Service engineers, contactors and other trades all need to at least be able to view the structure and piping and to be able to query the database with relevant questions. In the early days of CAD, the concept of layers was introduced. No real standards were adopted industry wide but normal practice lead to different layers for grid layouts, roadworks, dimensions, walls, windows and so on. A special form of ”query” is to ask the modelling software to do the ”drawings” – framing plans, connections and shop drawings for itemized components. If one reflects on this, the whole design process is reversed to the early days when suitable drawings were needed to build up a picture of the final structure. Shop drawings were commenced when everything else was finalized. Now drawings can be produced almost at any stage of the modelling
Page 146 LSAA 2007 Surfers Paradise Oct 25/26 Lightweight Architecture Stretching Our Boundaries Internationally process. Extra information can be added to the model without having to find some real estate on a sheet of paper to add notes or specifications. Different trades can ask for whatever drawings and data they need and get it from a centrally stored model. In the 1990s, several well established CAD packages had to be re–written when the demand for working in 3D grew. Newer systems appeared which could target specific areas like steelwork. A lot of the development in computer applications has been driven by architects and their need to visualize the completed building environment. Great steps were achieved when hidden lines could be removed. Various techniques for shading surfaces became common and the demand soon followed to be able to model the optical and textural properties of surfaces such as windows, carpets, floors and walls. It has been my observation that students of architecture often have computing skills in advance of engineers. As a student in the 1960s, a major first year subject was engineering drawing but the present skills possible with computer modelling of buildings or infrastructure does not seem to rate highly. Some of this is because of the lack of direct practical experience of academic staff and the pressures by accreditation bodies to insist that a significant proportion of courses is devoted to ”management” and the ”environment”. So, we have arrived roughly at the present situation. The figures below show the transition from physical to virtual models by computer. Computers are an essential part of our daily life and design work. Certain levels of computer skills are taken for granted although I have only met one or two people who can use a word processor correctly!
Current Industry Issues To a certain extent, the current industry issues are reflected in part by the content of the MSAA/LSAA Conferences and Symposia held since inception and a quick summary follows: H In the inaugural meeting in 1981, fire was discussed as several projects comprised atriums. In most cases, the fabric roof had a gap between it and the structure underneath and smoke could escape. H The 1984 Conference had several technical papers on fabrics – predominantly PVC coated fabrics originating in Europe H In 1985, fabric durability was covered along with wind loadings on structures. H 1988 and 1989 saw discussions on material behaviour continue and Bernie Davis gave some insight into fire and the requirements of AS 1530
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H In 1990 the MSAA presented some sponsored research results of wind pressure coefficients on a range of conical structures H In 1991, Peter Lim talked about fabrics mentioning silicon coated fabrics and foils – both getting a revisit at the present conference H Mike Lester and Peter Kneen talked about computer software for determining patterns from 1993 H Tristram Carfrae covered high technology glazing systems in 1994 when the MSAA expanded its range of structures and became the LSAA H A number of exciting and larger projects have been presented at most meetings and today we have seen that many of the projects are of truly world class and have been designed by members who have grown up with the industry from the early days H One of the first such projects presented by Ian Norrie in 1994 was the innovative Hong Kong stadium using long span arches – interesting to see how often this design concept has been adopted since. So what remains as issues for the industry and for LSAA to address? Fire Fire is the current hot topic and needs to be studied in an objective manner. It would seem that because of the wide range of unusual structures designed, an all encompassing prescriptive based code or regulation is not advisable. There is more to it than fire tests on pieces of fabric. The codes AS 1530 Parts 1, 2 and 3 have the latest versions dated as 1994, 1993 and 1999. There is considerable pressure to update standards every five years so by this criteria alone, the industry should be prepared to contribute. The Building Commission of Australia is now a driving force for change and we must work cooperatively towards a workable outcome. For many steel structures, where fire is also an issue, there are deemed to comply approaches but also there is the chance to have a proper fire risk assessment made of a given design. This may lead to a detailed assessment of safety and maintenance procedures, alarm systems and so on. It is known that computer simulation of panic situations and demands placed on emergency exits have been used and some solutions such as increasing stair and door widths can markedly change escape times. The basement bomb scare on the World Trade Center in the 1990s saw evacuation times of many hours (10+) but with subsequent evacuation drills and procedures, these times were reduced to an hour or so – perhaps the main reason why casualties in 2001 were relatively low. The casualties would have been much lower still but for communication confusion and the opposing traffic on the stairs with fire personnel trying to go up and tenants going down. Perhaps increasing the width of these stairs by 600mm would have helped enormously. Many permanent fabric structures have the fabric some distance away from being easily accessed – usually a large roof is much higher anyway but otherwise for vandalism reasons. The fire load is low because there is little in the way of material to burn (even if it does) and there is likely to be an escape path for smoke built in for ventilation anyway, or created if there is a sustained flame close to the fabric creating a hole. On the other hand, many temporary enclosed pavilions may have walls made of fabric and may be expected to have reasonably high numbers of people who are visitors and therefore are not in a position to study evacuation procedures. The high strength fabrics are tough and
Page 148 LSAA 2007 Surfers Paradise Oct 25/26 Lightweight Architecture Stretching Our Boundaries Internationally it would be difficult for occupants to simply tear the walls down. Of course there could be the perception that this could be done and may lead to a stampede towards the side walls with people being crushed. Having highly visible sharp cutting equipment (Stanley knives or similar) next to regularly placed fire extinguishers would be one suggestion. The other is for wall panels to be affixed using prequalified connections which would fail under crowd loading. Education The successful projects involve assembling a talented team where everyone can make a contribution and respect the contribution by others. Very few people have the complete range of skills to design these structures. There has been virtually no teaching of lightweight structures in Australian Universities other than during the Sedlak / Kneen era at UNSW or by isolated guest lectures by several of our members. It is encouraging to see the recent developments at UNSW with the new Architectural Engineering course as described by Zora Vrcelji earlier today. As hinted in my paper above, the expertise of academic staff in the area of practical design skills with lightweight structures is lacking and it is this area that perhaps the LSAA could contribute. It is probable that this is well beyond the resources of the current LSAA but maybe a case could be made for a Government grant. Marketing of Australian Capabilities The LSAA website has recently featured company profiles for its financial members. It is known that hits on our site have been steadily increasing and more work could be done to further promote our members. The company profiles could be extended into an industry capability matrix where all the skills and resources are indexed. Again, this work would require funding and planning. There may well be some scope for assistance to industry bodies by the Government as illustrated by the talk by Jeff Turner yesterday. Through the LSAA Design Awards there is the potential to publicize our industry and there may be opportunities to be developed with the RAIA and IEAust. Design Tools This paper has described the enormous strides in computer technology and software that has taken place. It would seem that the LSAA should consider as a major theme for a future Conference the design tools used by the industry – architects, engineers and fabricators. It is suggested that this could attract a much larger audience and sponsors. It would lift the profile of the LSAA. A particular issue with these tools is cost which is relevant for smaller operators / fabricators that find it difficult to justify engineering or specialist design input for small projects. Unfortunately these small projects may require certification and have warranty implications. An appendix lists some of the software found by a simple internet search – no checking was done on the relative merits of any particular program. Concluding Remarks This paper has been a walk down memory lane looking mainly at the evolution of computer technology and software applications and how these changes have aided the design process. There remain some ongoing industry issues which have been briefly described.
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Appendix – Some Software Links (reproduced from a Google search)
H Easy Complete engineering design of lightweight structures. Force equilibrant formfinding. Geometrically non–linear load analysis. Cutting pattern generation. Visualization. (Technet GmbH). H Surface is a program that allows you to create your 3D tent membrane shape and then works out the shape of the panels that must be cut out and joined together to form that 3D shape. You can either create the shapes directly in the program using the powerful features that allow you to modify the shape by altering tensions within the membrane and it’s supporting ridge, valley and edge cables or if you have already developed the shape in other conventional CAD systems you can make use of the extensive patterning and geodesic panel edge finding features of Surface to create any panel arrangement that you want. (Surface Software). H Patterner is a powerful collection of tools for working with 3D surfaces. Patterner is primarily for the design and manufacture of tents and fabric structures. Powerful manipulation and drawing creation tools make it useful for anyone building complex 3D forms from sheet materials. (Rudi Enos Design). H Surface Evolver is an interactive program for the modelling of liquid surfaces shaped by various forces and constraints. The program is available free of charge. (Ken Brakke). H ForTen is the first commercial software specifically developed to calculate and model tensile and fabric structures. Forten is both a geometrical and mathematical modeler that permits to you to obtain the exact building shape, starting from free form 3D mesh, joint conditions or stress conditions. (Europe Engineering Division). H The Tentnology CAE program provides an easy–to–use solution for design and analysis of tension structures. Operator can generate 3D models of a concept, then apply wind and snow loads to view force, reaction and stress. When satisfied with the results, the user can readily produce cutting patterns for manufacture. (Tentnology). H MCM–lite is the hassle–free software that lets you create tensile membrane and cablenet structures without mastering complex engineering principles. The complete engineering version of MCM is also available on a limited basis to professional engineers. This version includes full analysis capabilities – large deflection finite element method analysis. (Birdair). H Engineering Pte Ltd provides a suite of programs for design (according to British standards) and analysis of tension structures: WinCable for cable and cablenet design and analysis and WinFabric for tensioned membrane structures design and analysis.
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